Sam Khalaf and his son Riyadh used to call themselves the two musketeers. When Riyadh was growing up in Bray, south of Dublin, they were inseparable. Like twins or best friends, they say. So the Iraqi-born, Irish citizen remembers keenly the moment when he realised his eldest child had drifted from him.

“We used to go everywhere together,” 54-year-old Sam recalls. “Every weekend we’d go to a tropical fish shop and pick out which koi carp to go into our pond. The first time Riyadh didn’t come with me, he was about 15. And the lad who worked there said: ‘Where’s your mate?’ I said, ‘He’s grown up now, he’s out with his friends.’ It was a shock to the system.”

The bigger shock was yet to come. Riyadh had stopped hanging out with his dad because he realised he was gay – a revelation he did not think his Muslim father, a garage owner with a passion for football and cars, would take well.

He was right: it took him another year, and when Riyadh came out to his dad, Sam says it “came like a fast train, it hit me very hard. Those couple of words didn’t register. I was going, ‘Shit, is he? Fuck, fuck!’”

The coming-out drama forms part of a new book by Riyadh, an Irish YouTuber and broadcaster, whose bright, conversational guide to being a young gay man – Yay! You’re Gay! Now What? – offers salient advice on topics from gender identity to anal sex. There is also a necessary chapter written from the parents’ perspective, by Sam and Riyadh’s mother, Lorraine.

We meet in Riyadh’s flat in London. Both men are as candid as the book, particularly with each other. Riyadh, 28, recalls that he was flamboyant as a child. In his book, he writes that, “I was king of the sissy boys, growing up. I loved running around the house in my mother’s pink silk nightgown, black stilettos and anything I could find that sparkled.” At seven, his father told him to start acting like a boy. “I was worried he was too gentle, I needed to toughen him up,” Sam says now. When Riyadh was in his early teens, in addition to hiking or fishing, his dad took him to karate. “I thought, he was going to get the shit beaten out of him, so I wanted him to toughen up. I saw him as soft.”

Riyadh read this as a judgment. “We’d been buddies so closely until that point and then, all of a sudden, I wasn’t enough. I hadn’t got enough masculinity in me to match what you saw as normal or acceptable,” he says, addressing his father directly. “I knew you were doing it because you were worried about my safety in the big, bad world. But it was damaging because I couldn’t live up to the expectation. It wasn’t me.”

Riyadh told his father over dinner one evening, writing 'I’m gay' on a piece of paper and handing it over

Sam had toughed it out himself. Born in southern Iraq, he lived in Baghdad until 1982, when an error on a reissued birth certificate (three years were knocked off his age by mistake) gave him a window of time to escape the country before military service beckoned. “Friends of mine lost arms and legs. Some died,” he says of the Iraq-Iran war of the time. “You walked down every street, and there was a funeral.”

He had always hoped to go to Europe (“I loved the way people could live freely”) and on his second attempt he reached England, where he met Lorraine, a Catholic woman from the east coast of Ireland. They fell in love, married and moved to the seaside town of Bray, where they had their first son, Riyadh, two years later.

At 16, he came out to his mother after she found gay porn on the family computer. She kept her son’s secret from his father for nine months. “She was my shelter and my confidante,” Riyadh says. She was also adept at making his sexuality the new normal. Driving around in the car together, she used to point to a good-looking man and ask: “Would you?”

During this time, Riyadh’s relationship with his father soured. “I hated him for what he didn’t already know,” Riyadh says. Lorraine told her son to tell his father over dinner one evening. Riyadh wrote down “I’m gay” on a piece of paper and handed it over. Sam was bewildered. “My head was like a washing machine,” he says now. “I was acting, pretending I was OK. I always try to fix things if something is broken.”

Now he couldn’t find a fix. He decided on drastic action. “I got up and sat in the back garden at 3am. My head was absolutely wrecked. I searched the house for tablets.” He pauses, and his son asks him about those suicidal thoughts.

“Why did you not do it?”

“I couldn’t find them.”

Riyadh was also in a terrible state. He worried that his father – whom he describes as “outrageously heterosexual” – would instigate an honour killing or arranged marriage, or force his son into gay conversion therapy. In his book, Riyadh frames this lightly, as his own “super-dramatic thinking”. But he wasn’t far off the mark: Sam’s response was to put his faith and honour first.

Facebook Twitter Pinterest ‘Wake up,’ Riyadh’s mother told his father. ‘I know you love your son, so show your love.’ Photograph: Mark Chilvers/The Guardian

“I thought of family,” Sam says, “which is really stupid, because I left Iraq so long ago.” He breaks down at this, upset by the conflict his son’s confession exposed. Riyadh explains that his father spoke to a family member, and that it did not go well. “They asked, ‘How come your son is like this? You should change him,’” continues Sam, still in tears. “They said we could help Riyadh: bring him to Syria and treat him there with conversion therapy.”

Then Riyadh’s mother stepped in. “Lorraine said, ‘Wake up,’” Sam recalls. “‘I know you love your son, so show your love.’” She asked a neighbour who had two gay sons to talk to Sam. “A lovely man,” he says. “An absolute gentleman. He said, ‘Look, son, the family is you. Forget about what they [the wider family] think.”

He decided to rebuild the relationship with his son. Riyadh and his younger brother had been raised in a multi-faith household: they were brought up Catholic, like their mother, but also attended mosque with their father at weekends. Now the family began to reassess their relationship with faith. They made a collective decision to stop practising religion altogether and redefine themselves as humanists.

Riyadh stresses that he does not believe it’s impossible to reconcile sexuality with faith. For his family, it was a simple decision. “We as a family found it quite easy to step away from all religion because we were never very faith-led in the first place. We were, by default, following what we’d been told to follow from a young age. My coming out was a catalyst for us to stand back and look at those beliefs and ask, ‘Do they represent us as a family, or not?’”

Riyadh asks his father if this was difficult for him. “No. No. As long as I’m a nice person,” Sam says. “As long as I’m not going to hurt people or do bad things, I am just happy with that.”

Sam then cut ties with his wider family. “There is no relationship now. Because of Riyadh I have lost family members, but it is fine with me, honestly,” he says. “Once my two boys, my wife and I are happy in our home, I don’t care what is going to happen out on the street.”

Since Riyadh came out, Sam has been to gay clubs and on Pride marches and made new LGBTQ friends. But perhaps the most dramatic shift is in their relationship with each other: they are remarkably close, comfortable sharing anything.

There was no hesitation on Sam’s part when Riyadh asked him to help with the book. Riyadh’s involvement in the marriage equality campaign in Ireland had been crucial: “I could see my son going on the TV and radio, trying to help the Yes vote. You realise that he is actually saving lives and doing good. Now who wouldn’t like something like this?”

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Getting involved with his son’s activism – appearing together in YouTube videos, on Irish television, in the book – was a no-brainer. “This book – even if it saves one life, it would be worth a great deal,” Sam says. “If it’s going to help stop one parent or one father like me from considering suicide, it’s worth doing.”

The first LGBTQ event the Khalafs attended as a family was a Dublin rally for marriage equality in Ireland. “We were standing side by side. Dad was getting emotional, watching the speeches,” Riyadh remembers. “I couldn’t believe what I was seeing. He was cheering and shouting for the LGBTQ cause. It was like a personal revolution. It was like, ‘I won’t hate, I will love.’”

“You took the words out of my mouth,” says Sam. He turns to Riyadh and, with tenderness, says: “It’s because I love you, son, that’s why.”

In the UK and Ireland, Samaritans can be contacted on 116 123 or email jo@samaritans.org or jo@samaritans.ie.

• Yay! You’re Gay! Now What? by Riyadh Khalaf, published by Frances Lincoln, is out now, priced £9.99. To order a copy for £8.79, plus UK p&p, go to the guardianbookshop.com