It is 9.45am at the London Aquatics Centre. Tom Daley climbs up to the diving board, wipes the sleep from his eyes and yawns. Another day, another training session. In the adjoining pool, regular swimmers get on with their exercise. Today, Daley has an audience of one – me.

Three years ago he stood on this diving board in front of 18,000 spectators, winning an Olympic medal for Team GB. It was a bronze, but it felt as good as any gold. A diving medal is particularly hard to win: the competition is ferocious, particularly from the Chinese, and there is no margin for error. One bad dive and you’ve blown it. But there was more to it than that: there was the recent death of Daley’s father, the bullying at school and on Twitter, and the humiliation he had suffered in Beijing four years earlier, when his synchro partner Blake Aldridge (26 at the time) blamed the then 14-year-old for their failure to win a medal.

Has any British athlete had to do so much growing up in public? Daley’s lows, highs, puberty, A-level results – all were pored over by the media. After the 2012 Olympics there were stories that he was done with diving, that his coaches were complaining he was distracted by presenting the TV show Splash!, that he was throwing away his talent.

Then, in late 2013, Daley beat the tabloids at their own game: he came out, entirely on his own terms. Hardly unusual in 21st-century Britain, but still a rarity in sport. On his own YouTube channel, Daley announced he had something to say: he had fallen in love, and it just so happened to be with a guy.

Nineteen months on, Daley is more focused than he has been in a long time. He is training for the World Aquatic Championships (which start next week in Kazan, Russia) and, more importantly, for the 2016 Olympics in Rio. “I feel much more mature going into 2016 than 2012,” he says, having completed his morning diving session. We’re sitting in the auditorium above the diving pool. Daley has changed from trunks to shorts, salmon-pink T shirt and trainers, and is talking about why Rio should come at the perfect time for him. “Divers tend to peak between 22 and 24,” he says. “I’ll be 22, so I should be approaching mine. I am stronger now, jumping higher, spinning faster, moving quicker than I ever have. I’m in love with diving right now.”

It hasn’t always been this way. In 2011, his then coach, Andy Banks, who had trained Daley since he was eight, revealed that as a youngster Tom got so distressed away from his home in Plymouth he told Banks “I’d rather be dead than on this training camp”; once he threatened to jump out of a window if he was left alone. His father, Rob, gave up his job as an electrician to travel with him, and they became inseparable. But when Tom was 12, Rob was diagnosed with brain cancer; five years later, in 2011, he died aged 40. When Daley won his bronze in London, he held it up to the heavens. The message was clear: this one’s for you, Dad.

'Things were going really crap. There were times when I thought, "Oh God, I really can't believe I'm still doing this'

Daley went back into training 10 days after the Olympics, settled down to his final year of A–levels (maths, Spanish, photography), and found himself at a loss. “Once, every four years, you get an opportunity to compete in the Olympics. You have these six dives that decide whether you’re an Olympic medallist or not, which is quite intense. And to come down after that high of winning a bronze medal was pretty tough. I tore my triceps, was suffering loads of injuries and it was a really weird year. You ask any Olympian what the year after the Olympics is like – you always get the Olympic blues. Things were going really crap, and there were times when I thought, ‘Oh my God, I really can’t believe I’m still doing this.’ ”

At 18, he was already a veteran. Daley started diving when he was seven years old. He had shown promise in other sports: he was an able swimmer (he says the furthest he swims these days is to the edge of the pool after a dive) and represented Devon in judo when he was nine. Then he discovered the diving pool and that was that. “It looked really cool, seeing people do somersaults off the board. I enjoyed swimming and being in the water, but I got a bit bored with it and wanted something a bit more adrenaline-fuelled.”

Did it not terrify him? “No, because when you’re young you’re fearless – you don’t think about it, you just do it. And I loved it.”

Daley in training, aged 14, in the year he became Britain’s youngest Olympian at Beijing 2008. Photograph: Rex Shutterstock

The speed of his progress was astonishing. At 13, he became the youngest gold medal winner at the European Championships; at 14, he was Britain’s youngest competitor at the Beijing Olympics, and the youngest competitor in a final; at 15, he became Britain’s youngest world champion; and at 16 he won two gold medals at the Commonwealth Games. He is the only person to have won the BBC’s Young Sports Personality of the Year award three times.

But as the dives became more risky and ambitious, he did become frightened. He hits the water at 35mph, and has said that every time he dives it’s like a car crash. Even when he gets it right, it hurts. When he gets it horribly wrong, the consequences don’t bear thinking about. He says the fear is positive. “Every time you go up to the board, you get scared. It’s more like adrenaline, though – you feel pumped and ready to go.”

Today I watch Daley dive for an hour from various heights – a handstand here, a twist there, a couple of backward somersaults. Most of the dives are arrow-straight, with barely a splash as he enters the pool. Close up, it’s terrifying: the height of the top board (10m, or slightly taller than a typical two-storey house), the tippy-toeing on the edge, the way Daley appears to come close to hitting his head on the board as he comes down, the complexity. Before each dive he dries himself with his union jack towel; afterwards, he goes to the side of the pool to watch it on an iPad with his Zimbabwean-born coach, Jane Figueiredo.

'Every time you go up to the board you get scared. It's more like adrenaline, though – you feel pumped, and ready to go'

Diving takes enormous patience, as well as nerve and skill. The tougher the dive, the more points you can score. At the London Olympics, Daley’s final dive was marked down because the degree of difficulty wasn’t as high as his rivals’. It can take him three years to perfect a new dive. He is still working on one for the World Championships and the Olympics: three and a half forward somersaults and one twist, which he calls the Firework. He displayed it for the first time in competition at the British Championships in February, where he won the individual 10-metre platform for the fifth time. He is currently ranked second in the world, sandwiched between two Chinese divers – Yang Jian in first and Qui Bo in third. In London earlier this year, the Firework scored 99 points – his highest ever score for a twister dive.

After diving practice, Daley shows me around the “dry dive” at the London Aquatics Centre. It looks like a baby gym, with trampolines and bouncy foam areas to jump on. The jump is crucial in diving – the higher it is, the more time a diver has to complete the mid-air routine before spearing into the pool. To the side of the dry dive are massive weights – Daley squats 125kg and does press-ups with more than 80kg on his back. At the far end are the ballet bars that he uses to boost his core strength and toe point. Is he any good at ballet? “I’m no Billy Elliot!” he says. “I enjoy it, but it’s very hard. It’s definitely benefiting my diving.”

The training schedule is relentless. Daley does 11 sessions a week in the gym and dry dive, 11 pool sessions, and one session of ballet. Each session lasts between two and three hours. Then there’s the austere diet: egg whites and spinach and a bowl of porridge for breakfast, chicken and pulses for lunch, and salmon or chicken with steamed vegetables for dinner. Every day the same regime, same food, same 10pm bedtime. Daley currently has 6% body fat (most men his age average between 14% and 18%) and weighs 70kg. Before the World Championships start next week, he will lose another couple of kilos.

There’s more to diving than denial, though. There’s pain. Before heading back to the arena he gives me a guided tour of his scars. There’s the Harry Potter scar on his forehead (“I did a forward dive and dunked my head on the poolside on my way in. It looked as if there’d been a shark attack”), another scar on the top of his head, and a strange lump where he tore his triceps.

All this training, all these injuries: how much do you have to want it to succeed in diving? “Oh, you have to want it more than anything. You have to be willing to miss out on everything. It has to be the biggest thing in your life – otherwise why would you do it?” He pauses. “Why would you?”

'I guess it has always been in the back of my head I might be gay, but you never know'

What are the biggest sacrifices? He doesn’t know where to start: “Staying out with my friends. I have to be in bed for 10pm, so I can get enough hours’ sleep. I have to sacrifice going out and eating what I want. I haven’t had a drink since September. The thing I miss the most is the freedom just to be able to go and do something during the week, or if I want to go on holiday for a week in, say, April. Things like that just don’t happen, because I’m training all the time.”

After London 2012, he asked himself the “Why would you?” question more intensely than ever, and couldn’t come up with an answer. He’d won his bronze, he’d got two As and an A* in his A-levels, he had his own TV show, and yet he felt stymied and frustrated. Perhaps he hadn’t properly mourned the death of his father, perhaps it was that he’d never let himself go like most teenagers, perhaps his hormones were playing havoc. “I felt down. I’d been on that high and you come crashing down. I knew I had to try to get myself out of the rut.”

In the summer of 2013, after the World Championships, he and his schoolfriend Sophie Lee strapped on their backpacks and set off on a world tour: “Thailand, Japan, New Zealand, Australia, Spain, France, Switzerland, Morocco, California, Texas, Haiti, Jamaica.” He recites the list, then gets frustrated when he temporarily can’t remember the final destinations. “Ah, yes: Florida and Mexico.” Even then, there was work involved. The trip was filmed for an ITV show, Tom Daley Goes Global.

Daley with his boyfriend, screenwriter Lance Black. Photograph: Getty Images

How long did all that take? “Six weeks,” he says. Blimey, I say, so you squeezed a gap year into six weeks? “Yes. I like the fast pace of it all, because that’s what my life is. It was good to do that trip and get it out of my system. It made me think, OK, I’m not missing out too much. I’ve done that stuff – I can go back to diving now.”

He decided to leave his home in Plymouth for London and a new coaching setup. “When anybody my age would have gone to university, I moved to London and changed scenario. Things just felt different and fun again.” And it is all this, he believes, that has resulted in the finest diving of his life. This, and one other thing. “I think I’m diving as well as I am now because of Jane, and because of Lance.”

In March 2013, Daley went for dinner at a friend’s home in Los Angeles and met Dustin Lance Black, a screenwriter 20 years his senior who won an Oscar for Milk, the biopic of gay rights campaigner Harvey Milk. Daley says it was love at first sight. Until then, his only relationships had been with girls, but he had never been in love. Had he thought he might be gay? “I guess it has always been in the back of my head, but you never really know. I’d never had feelings for a person along those lines. I’d been in relationships with girls where I’d had sexual feelings, but it became so much more intense when I met Lance. I thought, ‘Whoa, this is weird. Why am I having these feelings for somebody?’”

Did that freak him out? He nods. “It freaked me a little bit initially, but then it was like, ‘OK, this makes sense’. Lots of things started to make sense.”

Is this his first relationship…? He cuts me off before I can finish the question.

“With a guy? Yes.”

Does he think he’s unusual in discovering his sexuality so late? Well, he says, it’s more complicated than that. “I always knew that I had that attraction to guys, but I just thought that was a usual thing, being attracted to guys and girls. It was only when I met Lance I started having such strong feelings.”

Black and Daley texted each other for two months; Black came to England for Daley’s birthday, and they became an item. Black now spends most of his time in London.

Tom Daley: ‘At some point in my life I’d love to be able to settle down and have kids. Get married and lead a normal life’ Photograph: Ben Quinton for the Guardian

Black has played a key part in the US campaign for same-sex marriage. “In 2009 he made that Oscar speech, saying he would get marriage equality all across America – and now there is marriage equality across all 50 states. They say it happened 10 years quicker than anyone thought possible,” Daley says, proudly. How influential was Black in achieving that? “Well, he was the one who took the lead with a guy called Chad Griffin [co-founder of the American Foundation for Equal Rights], and they took it to the next level. He doesn’t like to say he’s done it because he’s too modest, but he is one of the biggest reasons it’s happened.” Daley is blushing with pride. He admits he knows next to nothing about movies, and hadn’t even heard of Milk when they met. “It’s actually really good,” he says of the film, as if I’d be surprised.

Did Black encourage him to come out? “Yes, he was supportive, but it never got to a point where he said, ‘You should do something about coming out.’ He was just always there, supportive. At no point was he at all pushy.”

Did he discuss coming out with his mother? “Oh yes. My mum had known for six months, and so had my friends. Mum was like, ‘Whatever makes you happy, I’m completely OK with.’” It couldn’t have been more different from the reaction from Black’s family. “He was Mormon, so homosexuals were put in the same group as serial killers.”

Daley says he was unsure how, and whether, to come out publicly right until the last moment. “I thought, should I just not say anything and get caught out, which would be horrible?” And would he have regarded it as getting caught out? “It was more a case of, ‘Oh screw it. I don’t care what people think. I’ll do my own thing. I can still dive, I can still do what I want to do.’ Then I was thinking I could do a newspaper interview, but you wouldn’t want somebody to twist your words. You could do a TV interview, but you don’t want to be asked questions you don’t want to answer. So I just said exactly what I was comfortable with saying at the time. And nothing could be twisted.”

Was there anybody directing him when he made his video? “No, I did it on my phone. I was the only one in the room. That was the way I talk to people anyway, through my YouTube channel.”

How did he feel once the video was out? “It was a massive weight lifted off my shoulders. I was terrified before. And then when it finally happened I was like, great, I don’t need to worry about it any more, people know, who cares, whatever…”

Daley comes out, on his YouTube channel, in late 2013. The film has since had more than 11 million views.

He was amazed by the reaction. “It was so nice how accepting people were.” They were a bit more than accepting, weren’t they? (Within a day of being uploaded, his video had been viewed 4.5m times; the equality organisation Stonewall said he was “a role model for thousands of other young people”, while Lady Gaga called him “inspiring”.) “Yes,” he says quietly. “People respected it, I guess.”

In the video he said he was also attracted to girls. Does he consider himself bisexual? “I don’t put a particular label on any of it because right now I’m in a relationship with a guy, but I still have sexual feelings towards girls.”

Does Black mind? “No, we joke about it sometimes. He actually sometimes has sexual feelings towards girls. Relationship, feelings… I’m with Lance, but you can appreciate anyone who’s hot!”

Daley has since become a campaigner in his own right, teaming up with the LGBT support line Switchboard. “I’ve been lucky in having friends and family to talk to. Lots of people don’t have that, because if they told their family they’d be kicked out on the streets.”

We talk about how hard it is to come out in British sport. “But I think less and less so,” says Daley. “Nobody batted an eyelid when I did. Nobody cares. I think lots of people do worry in sport, but they would be so surprised if they did come out. I don’t think it is as big an issue as people think.”

I point out that the footballer Justin Fashanu is still the only top-level British footballer to have come out. That was in 1990, and he killed himself eight years later. Is it harder for footballers? “I think there’s fear for anyone no matter who they are. And if they have to do it on a scale where lots of people are watching and judging, it makes it even harder.”

What advice would he give a gay footballer? “I would say, if you come out, they can’t take away how you play football. That was the thing for me: once I did come out, it’s not going to affect my diving. I can still perform, no matter what anybody else thinks of me. I’m judged for what I do in the diving pool. And footballers are judged for how they play on the football field, not anything else.”

What about if you don’t come out: can that affect your sport? He nods vigorously. “Yes, because you can panic about it. It can be in your head; it becomes a bigger thing than it needs to be. So yes, definitely.”

I first interviewed Daley four years ago, and the difference is striking. Back then, he seemed weirdly old for his age – 17 going on 40, so polite and proper it was unnerving. Today, he is still old for his age, but in a much more natural way – maybe 21 going on 30. I remember thinking his life experience seemed so limited, even for a 17-year-old – it didn’t extend beyond his much-loved parents, the younger brothers he’d play-fight with, diving and school. Now he has a hinterland. Black has introduced him to a new world – of activism, LA, the arts. The couple featured in David Hockney’s most recent work, and the diver still can’t quite believe it. “I researched David Hockney for my A-level photography project. He’s great. Then we went to have lunch with him at his studio, and he was like, ‘Oh, just stand there and I’ll take some photos.’” So now they’re friends? “I wouldn’t say we were best buds who go down the pub, but we’ve had lunch twice.”

There is still something grounded and endearingly old-fashioned about Daley. You sense it must be rooted in his family. He remains close to his brothers, who are singularly unimpressed by his achievements (or so they tell him), and he cites his father as his hero. “I try to live by all the lessons he taught me. He always used to say, make sure you go out of your way to help someone every day.” At times he sounds like a throwback to a previous generation, not least when talking about his responsibilities towards his mother. “I feel like I’m in charge and have to look after her, but she’s so independent. She’s doing really well.”

Daley celebrating his bronze medal at the 2012 Olympics. Photograph: Getty Images

Daley is one of life’s planners, and he’s already mapping out the future – a gold medal in Rio, a future in television (he has to work because there is still no money in diving), and family. “At some point in my life I’d love to be able to settle down and have kids. Get married and lead a normal life,” he says.

Look, I say, I don’t want to put the pressure on, but Lance is already 41. He laughs. “He’s getting on! I don’t know – right now I’m focusing on the diving. It could be in a year, five years, 10 years. I’ve always loved the thought of having kids. Boys could be easier because you don’t have to worry as much about them… As girls get older, you worry about them more, I think. Ideally I’d like to have one of each.” A second later he changes his mind. “Two of each.”

What would he be like as a dad? “I’d like to think I would be fun, but also try to teach them all the lessons they need to learn, that you don’t get anything without hard work – I’d like to pass on the lessons I had in my childhood.”

Who would be the tougher disciplinarian, him or Black?

“Me.”

“Why?”

“Because Lance is a massive softy. He’s very strict at his work, but people he loves, he finds it very difficult to say anything. He wouldn’t be able to shout at the kids or tell them off.”

Tom Daley: ‘I’m feeling good about going into the world championships, feeling good about the Olympics next year, things outside diving are going really well.’ Photograph: Getty

So you’re 20 years younger, yet you’re the boss? “Yeah!” He grins. “Well, I have to be. Somebody has to be.”

The great thing about their relationship is they are not dependent on each other, he says. “It makes it so much easier, being with someone who gets having to work really hard, and gets how we have other things in our life that we want to be successful at,” he says. “And we’ve both worked really hard all our lives to get things we want. I want an Olympic gold medal; he wants a smash hit in the box office or a really good film.”

It’s lovely to see you so at ease with yourself, I say. “Well, touch wood,” he says. “I keep saying that, because anything can go wrong at any point, but – touch wood – things are going really well right now. I’m feeling good about going into the world championships, feeling good about the Olympics next year, things outside diving are going really well.”

Anyway, he says, if there ever were any danger of him getting carried away, he’s always got his family to bring him back down to earth. “D’you know the first thing they said after I got bronze at the Olympics? ‘Ha ha, you came third!’ ”