Go home, a voice inside me said. Decline with a polite smile and go home now. And maybe I would have if I hadn't liked her so much.
Maybe I would have if it hadn't been such a rough night. Maybe I would have if I wasn't coming up to thirty.
Maybe I would have if her legs had been a couple of inches shorter.
'Okay,' I said, far more casually than I felt. 'Sounds good.'
She looked at me for just a moment, and then we were kissing each other, her hands on the back of my neck, tugging at my hair with small, urgent fists. That's strange, I thought. Gina never does that. five A chHd can change in a moment. You turn your back for a couple of seconds, and when you look again you find they have already grown into someone else.
I can remember seeing Pat smile properly for the first time. He was a little fat bald thing, Winston Churchill in a Babygro, howling because his first teeth were pushing through, so Gina rubbed some chocolate on his sore gums and he immediately stopped crying and grinned up at us -this big, wide, gummy grin - as if we had just revealed the best secret in the world.
And I can remember him walking for the first time. He was holding himself up by the rail of his little yellow plastic stroller, swaying from side to side as if he were caught in a stiff breeze, as was his custom, when without warning he suddenly took off, his fat little legs sticking out of his disposable nappy and pumping furiously to keep up with the stroller's spinning blue wheels.
He bombed off out of the room and Gina laughed and said he looked as though he was going to be late for the office again.
But I can't remember when his games changed. I don't know when all his toddler's games of fire engines and Postman Pat videos gave way to his obsession with Star Wars. That was one of the changes which happened when I wasn't looking.
One minute his head was full of talking animals, the next it was all Death Stars, stormtroopers and light sabres.
If we let him, he would watch the three Star Wars films on video all day and all night. But we didn't let him - or rather Gina didn't let him - so when the television was turned off, he spent hours playing with his collection of Star Wars figures and grey plastic spaceships, or bouncing on the sofa, brandishing his light sabre, muttering scraps of George Lucas storylines to himself.
It seemed like only the day before yesterday when nothing gave him more pleasure than his collection of farmyard animals - or 'aminals', as Pat called them. He would sit in his bubble bath, a little blond angel with suds on his head, parading his cows, sheep and horses along the side of the tub, mooing and baaing until the water turned cold.
'I'm taking me bath,' he would announce. 'I need me aminals.'
Now his aminals were collecting dust in some forgotten corner of his bedroom while he played his endless games of intergalactic good and evil.
They were a lot like the games I could remember from my own childhood. And sometimes Pat's fantasies of brave knights, evil warlords and captured princesses sounded like echoes from a past that was long gone, as if he were trying to recover something precious that had already been lost forever. Siobhan slept like someone who was single.
She edged right into the middle of the bed, her freckled limbs thrown out every which way, or she rolled over on her side, taking my share of the duvet with her. I lay there in that strange bed wide awake, clutching a scrap of sheet the size of a handkerchief as the room got light. It was too soon to feel really bad. Pushed to the back of my mind there was the thought of Gina and all the promises I had ever made to her - promises from the days when I was trying to persuade her to love me, the promises we made on our wedding day, and all the promises of all the days beyond, all that stuff about undying love and never wanting anyone else that I had really meant at the time. And still did, I discovered. Now more than ever, in a funny sort of way. Later, this would all really get to me, and driving home I would look in the mirror wondering when I had become the kind of man I used to hate. But now was too soon for all that. I lay there as the night faded away thinking to myself - well, that seemed to go okay.
The reason that most men stray is opportunity, and the joy of meaningless sex should never be underestimated. It had been a meaningless, opportunistic coupling. That's what I had liked most about it.
What I liked least about it was that already I was starting to feel like a traitor.
And it was far from great. You try too hard with someone new. You try too hard to truly enjoy yourself. Sex with someone new is too much like taking your driving test. Yet when I thought of all the things that could have gone wrong - and all of them seemed to involve timing - it was okay. Thank God, thank God, thank God.
But all the time I was with Siobhan, while half of me thought that this was probably the woman I hadn't realised I had been looking for all my life, this pale Irish beauty who would have lovely red-headed children, the other half of me sort of missed my wife.
I missed the easy familiarity you get with someone who you have been with for years. If I was going to be unfaithful, then I kind of wished it could have been with Gina.
Still, you can get tired of always being the man who pays the mortgage and calls the plumber and can't put together the self-assembly furniture. You get tired of being that man because in the end you don't feel like much of a man at all, more of a domestic appliance.
So you go home with some stranger who doesn't let you have your share of the duvet and end up feeling more tired of yourself than ever. Now what did I do with my trousers?
Daylight was creeping into the room as I got dressed, and glimpses of Siobhan's life floated into view. It was a good flat - the kind of comfortable, ordered flat I had always wanted but never had. I seemed to have gone straight from student squalor to domestic disorder.
The only photographs I could see were of Siobhan as a teenager, laughing as she held on to grinning dogs or some sweet-looking old people. Pictures of pets and parents.
There were some Japanese prints on the walls, of peasants struggling through a rainy landscape - stuff Gina would have liked. Shelves neatly stacked with books and CDs revealed a taste for literature that had made it to the movies and a weird mix of rock groups and mellow jazz - Oasis and U2 next to Stan Getz, Chet Baker and the softer side of Miles.
Looking at her books and records made me like her more. But probably looking at anyone's books and records will make you feel that way, even if they have lots of rubbish. Because what they like, and what they used to like, reveals things about them that they wouldn't normally choose to advertise.
I liked it that Siobhan had probably grown out of white rock bands and was now looking for something a bit more cool and sophisticated (it seemed unthinkable that she might have started out on Chet Baker and Miles Davis then later switched to U2 and Oasis). It showed she was still really young and curious, still discovering what she wanted from the world. Still inventing her life rather than trying to recover it. It was very much a young single woman's apartment, the flat of a girl who could please herself. Despite the magazines and clothes that were strewn around, there was none of the real mess and clutter that you get in a place with a child, none of the homely chaos I was used to. You could make it all the way to the door without stepping on a Han Solo figurine.
But I sort of missed all of the clutter and mess that I knew from my home, just as I already missed being the kind of man who knows how to keep his promises. Gina was crying when I got home. I sat on the side of the bed, afraid to touch her.
'It was crazy after last night's show,' I said. 'I had to stay at the station.' 'I understand,' she said. 'It's not that.' 'Then what is it?' 'It's your mum, Harry.' 'What about her?'