Then I went out with Sarah for two years, starting in our third year of uni, before she left me for a guy she met at the office where she worked.

After a long period of involuntary chastity, I had a brief thing with a woman called Karen, ten years older than me, whom I had met through Victor. Karen and I both had meetings at Victor’s office at the same time and had got chatting while waiting in reception. Victor had found our tryst highly amusing and, until we split up, made constant jokes about being guest of honour at our wedding.

Karen was by far the best in terms of passion and technique, until Charlie came along. Karen and I had been an unlikely match: she was experienced, worldly, at ease in her own skin, while I was gauche and awkward. I’m still not sure what she saw in me. Enthusiasm, perhaps. Energy. She had recently split from her long-term partner and, even when we were having sex, seemed sad. Beautiful and sad. One day she told me she thought we shouldn’t see each other any more, and that was it. I ended our relationship feeling like a student who’d just graduated from a fun and rewarding course.

After that there was Harriet – who treated sex like a necessary bodily function – and then Charlie.

‘That’s it,’ I said. ‘My entire sexual history.’

She had been quiet as I had recounted my list. ‘And who was best?’ she asked.

‘You, of course.’

She didn’t smile. ‘No, I mean apart from me.’

‘Um . . .’ I told her it had been Karen.

‘The older woman. Are you still in touch with her?’

‘God, no. I haven’t seen her for years. It wasn’t that kind of relationship, where you stay friends afterwards.’

She cocked her head to one side, studying me with those big eyes. ‘What do you mean?’

‘Well, it was just . . . We met, we had a sexual relationship, then we split up. That’s all that relationship was about.’

‘Just sex?’

‘Yes.’ I cleared my throat. ‘I feel quite uncomfortable talking about it, actually.’

Charlie arched her eyebrows. ‘I find it interesting. I want to know everything about you. Don’t you feel like that about me?’ Beneath the water, she stroked my thigh, squeezed it.

‘I don’t know. I don’t really want to know your number.’

‘Really? Why not?’

The truth was, I didn’t want to know because I had this fear it would be too high. I knew that even if she’d had sex with one hundred men before me it shouldn’t matter. But I also knew that it would make a difference. That was just the way it was. I would rather not know. Then I wouldn’t have to care.

‘Because the past is the past,’ I said, resorting to cliché.