When my wife died at the age of 40 from a brain tumour in 2007, I remember going in a daze to the council offices with my four-year-old daughter to register her death. The certificate was laboriously scrawled with an ancient fountain pen, and the registrar solemnly asked me to check the details before signing it. I dragged my eyes through the words, which all seemed to make sense, until the bit about me: Relationship To Deceased; and then there was a word I couldn't make out. It should have said Husband, but I couldn't make the spidery blue marks on the paper form into that. I gave up and asked what it said. "Widower," he replied, clear and factual. And that was the first time I'd contemplated that word, in relation to me and my new categorisation in the world.

I'd known for three years that Katherine was going to die ("It will come back," the surgeon had said), because this was a recurrence of a particularly aggressive kind of tumour. But nothing really prepares you for losing someone so vibrant at such an early age. And you don't, somehow, think about that word. Until it happens to you.

As it turned out, being a widower provoked a maelstrom of unexpected emotions, not just in me but also in others. After a couple of weeks, I was back on the school run, which was almost embarrassing, being Banquo's ghost at the feast of chatter and bonhomie that is the playground mum gossip-fest. They all looked over, with pained and anxious sympathy, understandably almost resenting this massive downer that I had become.

And then I began to notice something different. After the initial discomfort, their sympathy genes quickly went into overdrive and I became the epicentre of a gaggle of empathetic eyes, kind offers of support, little encouraging pinches and hugs. And jutting, proffered breasts. Maybe I was a little bit insane, but the cautious body language of the playground seemed to become more insistent, less reserved, as if something normally fastidiously withheld, was on offer. "Widower" seemed to be taking on a surprising dynamic.

First out of the blocks was a lady who got me through the first few weeks, helping to deal with the almost impossible administrative burden of simply letting the children go to school. Nothing happened between us, but after a while I noticed that she had begun to stock her fridge with beers. Then a scrubbed-up divorcee began popping up asking if there was anything she could do. This created minor territorial issues between the two women, which I observed, bemused, from the sofa. I didn't particularly want to have anything to do with either of them, but on balance the first was less predatory and more helpful.

During the previous 23 years, I had been single for about six months. Living alone was surprisingly satisfying – if I tidied up the flat and then went out, it was still tidy when I got back! – but basically I've always sought that partner for life, as advertised in fairytales. From the age of 19 I had two six-year relationships. And then I met Katherine. I'd taken on a temporary office job on a glossy magazine, and there she was, coming down the stairs. The fairytale princess.

Within a month I had a full-time job there, and after three months she noticed me. The fault lines in both our relationships gave way, and I spent the next 13 years perpetually amazed that I'd found her. We were confident together, and she would often tease me about friends that she knew I liked. "Rachel was at the river today," she'd say, and my ears would prick up. "In a bikini." She auditioned male models as part of her job, and they regularly asked her out, so I had plenty of retaliatory material. It never occurred to either of us that we would one day have to look for a new partner, but we both accepted the possibility that, had we not met, we may have found someone else.

It's easy to deify the deceased, but Katherine was a special person. No enemies, no bad habits, no fillings. Her idea of a blowout was grilled fish and salad, and her grace and kindness pervaded everything she did. Audrey Hepburn crossed with Julie Christie, she was stunning at 28, but even more so at 40. I loved watching her age, which, like everything else, she did beautifully. I was not that surprised that she died. Why shouldn't she be chosen? It was as if she was put on Earth so that the injustice of her death could upset as many people as possible, God's sick joke, just to show that his ways truly are mysterious. Throughout her illness, I held on to the hope that experimental treatments could reverse her tumours. By the time her death was inevitable, it was too late to communicate with her properly, except emotionally. I cared for her at home, but there was no way to discuss the future, which loomed like a black hole.

About three months after her death, I was at a very low ebb. I desperately needed help with the children over the summer, so I advertised for an au pair. Most have the "No Father-Only Households" box firmly ticked, and I also had to come clean about looking after two children who had just lost their mother, which might not appeal. Eighteen rejections later, I got two positive responses. The first from an 18-year-old with a picture of herself in a negligee. Strikingly attractive, but clearly insane. The second was a short, succinct response from a 21-year-old studying for a masters degree in philosophy, with no picture, who simply said: "I feel for you in your situation. I think I can help."

That was good enough for me, so I booked her, even though she could stay for only two months. The children excitedly asked what she looked like and eventually hassled me into getting her to email a picture. Slumped, unshaven, probably unwashed, in my dressing gown, I watched it download, and it was as if a ray of sunshine had suddenly broken through the clouds. She was an absolutely gorgeous black girl with a kind, open face, and, it turned out later, that she earned extra money for her course by working as a bikini model. As a morale boost, this was looking good.

Despite her extraordinary physical charms, Farah's kind, thoughtful intelligence was what came through. She hit the small rural village where I live, which has a non-white population of zero, like a streak of black lightning. She had a Parisian chic that echoed Katherine's, and was exactly the sort of girl that Katherine would point out to me in the street so that I could ogle (Katherine's type was tousled-haired Latino men). I knew she would have been pleased for me.

As we spent time together, Farah's reassuring presence seeped into me. We spoke French, and I even struggled through her dissertation on Sartre. Gradually, our late-night conversations became more intimate, and we did that thing where you sleep in or on the same bed without doing anything for a while. When the inevitable happened, it felt very strange (after 13 years of sleeping with the same woman), but fundamentally right. Many friends were supportive, though some were appalled, and I don't expect an easy reception from readers. But I don't care. You don't know. You weren't there. Farah definitely took me from an extremely low point to somewhere different, the next step towards recovery. We both shed tears when I dropped her at the ferry after her two months were up.

Soon after this, I happened to read a novel that incidentally recommended that when you are bereaved, there are several things you should do. One was "sleep with someone exactly half your age". (I was 42 at the time.) At first I thought this was a flippant coincidence with my own experience, but then I heard about Peter, a friend of a friend who lost his wife about 18 months after I did. Within a few weeks, his 20-year-old European au pair was waiting for him in his bed. "And then the inevitable happened," says Peter (40). "But it was just nice having her around, some company. People disapproved, but she was very supportive."

Did he have problems with "bereavement tourism"? "I had a lot of that immediately after the death. It seemed to activate a mothering instinct; but it definitely focused much more on me than the children. And there was a definite edge to some of it. It seemed to make me more attractive than I should have been." To married and single women? "Yes, a complete mix. One of my wife's best friends started coming on to me really strongly. She's married, and amazingly she started before my wife died, and actually did it in front of her. Which obviously really pissed her off. After the death, she phoned me relentlessly. Once, she got drunk and kept coming over to try to sit on my knee, though her husband was there, and literally had to be dragged away by her brother and his wife."

Does he regret sleeping with the au pair? "No regrets at all. I'm still seeing her, in fact, but it's awkward now we live in different countries."

Meanwhile, as I had a reasonably high-profile job, letters started to come in from potential suitors. One lady was bereaved herself, but I didn't pursue it. Another offered her daughter, which was weird. But mostly, like Peter, I noticed the reaction of female friends, some single, some happily partnered and some not so.

Jamie, another friend who knows another widower, says, "In the aftermath, he used to call and say, 'I can fuck anybody.'" This is not a cry of liberation, but a declaration of turmoil. "An amiable flirt came round to offer support. She was a good friend and absolutely not his type, but something in him was saying, 'Now's your chance to touch her breasts.' He'd never wanted to do this before, and knew she was happily married with children. It was just a wild urge, but it took a lot of willpower not act on it. Soon he was stalked at the school gates by a married woman who quickly made herself indispensable and tried to move in. He couldn't believe it was happening, but she told her husband she was leaving and suddenly there was a complete mess. It's only now, eight years later, that he's settled with a proper girlfriend."

My first realistic prospect of a proper girlfriend was an ex I had dated before Katherine. Though she was incredibly supportive and a reassuring presence, after a while I think we both remembered why we'd split up. There was another six months with a 25-year-old journalist (kind, supportive), who kept making excuses to visit. In the end, she shocked me by declaring that she wanted to have children, right now. We'd had a fairly ruthless understanding about her vulnerability and my lack of long-term commitment, but she was so sad, and I felt awful watching her cry as she left. It was odd to have been so detached from the relationship between sex and real love. There was genuine affection, but it just wasn't the same as what I had lost.

In her book Why Not Me? Barbara Want talks about the disapproval when she experimented with a relationship after the death of her husband. There doesn't seem to be much advice on the web for widower sexuality, but one for widows has, I think, transferable advice. "You feel numb, but at the same time may also have sexual feelings that manifest in aberrant ways, like suddenly fantasising about having sex with a neighbour, which may be frightening. The desire to overcome loneliness is a major task facing widows. Each will confront it in their own way… some find comfort with other widows and single friends. Some venture into the dating world."

A psychologist friend agrees: "There are times when you just have to rebuild," she says. "One small block at a time, and not feel bad about thinking about yourself."

I've calmed down a bit now. The defining selection pressure in finding a new partner, I've realised, has been my defensiveness of the children. No one can replace Katherine, but anyone who comes into my life is viewed through the prism of what is right for them, a tough call because my standards are unashamedly high.

But there are nice people out there, and I think I may have found one. For a year I've been with someone who meets these standards, makes me laugh and is just nice to be around. Our initial bond was over bereavement. She lost a child and very nearly died in the process, and that means she understands things that other people don't. I think we've both taken each other to different places from where we were when we met. Which is all you can ask..