I don’t know how I’ve ended up standing on the doorstep of a long-lost friend, too scared to ring the bell. Well, I do. Last year my girlfriend Lucy and I decided to get married, and ever since one question has run over and over in my mind. Who can I ask to be my best man?

I’m not even certain I’m at the right house. Can it really be five years since I’ve been here? Prior to that, Owen and I met every week for tennis and coffee, over which we discussed work, films, books, relationships, just as we did in the sixth form, half our lifetimes ago. Last time I saw him, he was helping me move. We argued about politics that day and, after that, we both let the friendship slide. Now here I am, hoping to patch things up and ask Owen to be my best man. I’ve been trying to pluck up the courage to do this for months, but once again I lose my nerve and run.

Some people think devising the seating plan is the complicated part of organising a wedding. For me, it is finding a best man. At 35, I find myself with no close male friends. I haven’t fallen out with anybody, but I have allowed friendships to take a back seat.

I’ve been busy with work, with Lucy, with her friends, with family. Old friends are only a call or email away, but it never feels like the right moment to get in touch. The more time passes, the less likely it seems they’ll want to hear from me. It’s only now, when I’m forced to confront the situation, that I realise how cut off I’ve become. But am I the only one? Or are my friends, and other men my age, feeling the same way?

Growing up in Cornwall, I was fairly popular and played team sports. Ed, the scrum-half in the rugby team, was the drummer in my band or, as Ed might say, I played guitar in his band. At school we were a sarcastic duo, but we supported each other through our teenage trials.

Ed and I went to separate sixth forms, so I formed another band with Jack. When my first girlfriend dumped me, Jack listened to me drone on about my heartbreak. He fell out with his parents and came to live with us for a while. When I left for university, though, Jack stayed in Cornwall. In the holidays we picked up again and smoked weed on the beach. Gradually, I came home less and, whenever I did, I hurried past the fish restaurant where Jack worked, keen to avoid an awkward encounter.

I liked some of my colleagues but I never joined them for beers after work because I spent evenings writing book reviews

My best friend at university was David, who impressed me with his leather jacket and passion for Beat poetry. We chatted between lectures and, on winter mornings when my fingers were too cold to make roll-ups, he offered me his Marlboros. David encouraged me to ask out Lucy, our classmate, and before long Lucy and I were rarely apart. We graduated and together moved to Manchester, only an hour from David, so I expected to see him soon. But I never did.

In Manchester I met Tom, who was a few years older than me and already a successful playwright. On Tuesday evenings I went to his flat for Scrabble and always lost. Tom was a calm presence throughout my directionless, post-university phase, and I looked up to him. I hadn’t seen Tom for three years when, the morning after this year’s general election, he tweeted: “Shout out to everyone who decided to support the carve-up of the NHS. I hope none of you get the expensive kind of cancer.” In the pits of political despair, I remembered how comforting his surly wit had always been. But it had been so long, I didn’t even dare to click “favourite”.

Lucy and I moved to London, where I got a job editing a blog. I liked some of my colleagues but I never joined them for beers after work because I spent most evenings writing book reviews. Eventually, I left to try my luck as a freelance writer. Everyone, including me, was shocked when, on my final day, I burst into tears.

I thought I was crying with relief but perhaps, subconsciously, I was terrified. I was fed up with writing banal copy but, in a city where I was otherwise anonymous, there was something comforting about the office: its murmur of chatter, bleeping phones and familiarish faces.

Photograph: David Yeo

Three more years have passed in a blur of deadlines and I still don’t know anybody who isn’t connected to my work. If I nip out to buy wine on Saturday evening, I pass pubs full of people who look like they’re having fun. I see groups of men often catching up one-to-one, and I experience pangs for when my weekends were like that. Everybody except me has a fulfilling social life. Or does it only look like that?

I asked an expert. “Your experience isn’t unique,” says Professor Damien Ridge, who specialises in masculinity and men’s wellbeing at the University of Westminster. Friendships often drift in mid-life, he says, because it’s hard to stay in contact and your interests change – but he sees this more often in men. “You have to work at friendships, as you do in a relationship with a partner,” he says. “Loneliness in older men is a real issue, and many men in their 30s already show signs of heading that way. Compared with women, the men who see me for psychotherapy are emotionally isolated. I’m sometimes the only person they’ve opened up to.” He recognises similar traits in himself: “At a time in my life when I’m busy, I have to try really hard to keep friendships.”

Author Stephen Kelman’s novel Man On Fire was inspired by his friendship with Bibhuti Nayak, an Indian martial artist. Kelman, 39, contacted Nayak after seeing him in a documentary, with the idea of telling his story. They forged a deep bond over email and Skype, and Kelman has visited him in India twice. Kelman calls Nayak “my best friend”, but admits that he hasn’t been so successful with friendships closer to home.

“I haven’t kept up with people from school and university,” he says. “It wasn’t deliberate, just the way it works when your circumstances shift.” Now, he says, he’s trying to reconnect.

Dr Ian Williams, a GP and graphic novelist, empathises when I describe my failure to sustain friendships. “I’ve found this a problem over the last few years,” he says, “particularly after moving from the north to the south. I’ve lost touch with male friends with whom I was previously close. I fear I’ve pissed them off, although it may just be that they’re as bad at staying in touch as I am.”

I was lazy about friendships; I fell out of the habit of socialising and now I’ve forgotten how. So what do I do?

Is there a familial pattern? My dad hasn’t seen his boyhood best friend since he married my mum in 1972. “It was the summer we graduated and everybody went their separate ways,” he says. By contrast, Lucy’s dad plays golf with old schoolfriends, and her brother Neil, 38, had two best men at his wedding, one of whom he still sees every few months (the other has moved to Singapore).

The little socialising I’ve done in London has been with people Lucy knows, a fact I hadn’t even considered until now. “Men often rely on women to build the friendships around the relationship,” says Ridge. “If the relationship breaks down, then men can find themselves isolated.”

Once they’ve let friendships fall by the wayside, men can be less likely to attempt to revive them. Williams believes “male pride is very powerful” and thinks “women are much more likely to admit their vulnerability”. This chimes with what Lucy says, when I ask her what she thinks lies behind my predicament. “You never show people that you want to be wanted,” she says. “Instead, you wait for them to get in touch and, if they don’t, you forget them.”

And there’s more. “You’re terrible at keeping in touch,” she says. “You have no sentimentality. When I talk about how great university was, or express regrets, you say, ‘That’s done. Move on.’”

I can’t help feeling defensive, but I recognise what she is saying. I was lazy about friendships; I fell out of the habit of socialising and now I’ve forgotten how. So what do I do?

Dr Cosmo Hallström, fellow of the Royal College of Psychiatrists, who is in his early 70s, advises taking the long view. “Men are more career-orientated, striving and pushy in middle age,” he says. “When you reach my age, people who you haven’t seen for decades get in touch. By then, everybody has spare time.” Ridge, however, thinks matters are more urgent and suggests that I’m headed for loneliness later in life if I don’t start actively sustaining friendships.

Joe, a 37-year-old academic, advises keeping an open mind when it comes to invitations. “When my marriage was ending, I returned to England after several years in Brazil, and for three years I said yes to every invitation.” After that, there’s the small matter of keeping in touch with people once you’ve said yes. But aside from meeting new people, there’s the question of reconnecting with the old friends I’ve neglected.

Lucy keeps threatening to invite Owen to our wedding, because she knows I’m scared to do it, and that I’ll regret it if I don’t. I never returned after that failed attempt to casually drop round, but with two weeks to go until the big day, it’s now or never; so I call his mobile. When it goes straight to answerphone, I feel relieved, then disappointed, then sad at hearing his voice after so long, telling me to leave a message.

“Hi,” I say. “It’s Max, if you remember? I’d love to see you. Please call me. I have something to ask you.”

Owen calls back. “Sounds like we’ve both been hoping the other would make the first move,” he says. We laugh about this and the conversation flows as naturally as ever, which only makes our time apart more regrettable.

I don’t ask him to be my best man, but I do invite him to the wedding, and he accepts. He’ll bring his girlfriend, he says, with whom he’s been discussing marriage. He admits he feels a bit daunted by the prospect of organising a wedding, he says – and, especially, by the difficulty of finding a best man.

Some names have been changed.