I sit on the bench of the over-heated, over-crowded and under-clean swimming pool, watching my boys ignoring the coach's instructions. I am there partly because I like looking at these two little creatures who, an eternity ago - or so it seems - were in nappies and attached to my breast; partly, I confess, I wriggle in my seat like a hawk circling around its prey, examining the coach's muscles under the wet t-shirt he is wearing as he swims with his class.

Young men with that kind of physique should not be allowed to tease mothers of young children with wet fabric clinging to their sculpted bodies.

I know this particular coach, Mark. He is good-looking in a childish sort of way, tender and un-aggressive, a little like a Roman god's statue standing in a Georgian garden: safely and predictably handsome, given the age, job and surroundings.

I remember a particular incident involving Mark and a few women he was teaching, one morning. It was a small class of four doing floor exercises, and I was one of them.

'So, Mark, are you a qualified coach now?', honeyed one of the women, with the sleek and fit body of a thirty-year-old and the face of somebody twenty years older than that - a look shared by most of the ladies at the gym. She flashed her bleached teeth at him as the sit-ups started.

'Er... Yes, I passed my exams last month', answered Mark, between counting and throwing the ball at each of us, in turn, so as to maximise the amount of work our abdominals must perform. We looked like well trained, unlikely slim seals catching the ball as we came up, balancing on our bottoms, neck muscles as tense as violin strings.

Sometimes being so unbearably fit can also reveal ageing decay: this woman's completely flat stomach, displayed by her cropped top, curled up in three or four tiny folds of flabby, dry skin as she did her sit-ups with the mechanic prowess of an excavator. A crocodile in Lycra.

'So, what are you going to do here, now? Are they signing you up for a permanent position?' she cooed.

The sit-ups were so hard I thought I'd waste too much energy just listening to the conversation, when all my efforts had to be channelled into not stopping before everybody else. Competition can kill.

'No', replied Mark. 'I am still temping; they are retaining me as "casual staff".'

'Casual, eh? Did you hear that, ladies?' she snorted and smiled, lifting a carefully plucked eyebrow. She looked around trying to catch the eye of the others, to share the pun and fun.

Mark looked so desperately uncomfortable that I felt sorry for him. To be the object of women's unadulterated lust must surely be a very uplifting experience when you are barely twenty, unless they happen to be old enough to be your mother. I also felt embarrassed for Mrs Claws, with her plastic breasts and concave wrinkly tummy.

I had then collapsed under the ball Mark swiftly passed to me, the quicker to move away from her.

Now, looking at his body in the water, I check myself carefully for signs of inappropriate behaviour. Although I am not as old as Mrs Claw, there is something unsavoury about chasing young men like harmless gazelles during a safari. One should just admire their agile bodies without trying to grope them.

Besides, where is the fun with a man like Mark? He might be strong enough to make you pivot on one of his hands, but he cannot press any switches. Innuendos will just make him blush; at his age, he is hard-wired to kiss a fresh girl after the pub has closed and struggle with the clasp of her bra. No amount of verbal sparring is going to stimulate his sexual needs.

Nice legs though.

My thoughts turn to Master Pest n.1 and Master Pest n.2, their little bodies propelling themselves in the swimming pool with all the energy they can muster, grabbing life by its nano-second.

I look at them for signs that may remind me of their father; a facial feature, for example, or a mannerism. Are they not half of Mr Husband? Perhaps I can reach out for him by loving those children because they are his too.

But all I see is two cheeky faces, and I feel that they are very much mine and mine only. Maternal love can be the most selfish love of all.

I know that once they are in my charge again, after the class, I shall get cross when they do not wash, dry and get dressed as quickly as I would like; that they will manage, once again, to drop that large slice of pizza on their top; that they will ask and obtain a coin for the sweets, and then proceed to lose half of them in the short journey between the machine spewing the sweets out and the children grabbing them from the glittering little tray.

No matter how small the sweets, my boys' fingers are always smaller.

Somewhere in the building, Mr Husband is swimming alone, or perhaps showering by now. We live these parallel lives at the moment, whose trajectories occasionally meet so as to give him the opportunity to notice that the boys have E-colours all over their faces, necks and clothes, or that I have forgotten to lock the car in the car park.

Again.

Domesticity is a killer. The question is, can affairs provide a cure to prolong marriages, by accurately avoiding domesticity itself and thus making it more bearable, or do they distract from the parallel lives without changing their deadly nature or course?