Human Condition: Vain, fussy, demanding, disloyal - and she wonders why she's still single...

God save us from the whining, thirtysomething 'singleton', says Smug Married Aminatta Forna

THE WOMAN at the next door table was maudlin, weepy and in no mood to be comforted. She raised her finger and pointed at her companion and fixed her with an unsteady gaze. "It's OK for you," she pronounced, in a tone of bitter triumph, "you have no idea what it's like. You're married!" The other woman looked down guiltily. There was, apparently, nothing else to add.

This may yet be the most unsisterly observation I ever live to make, but the growing realisation that a significant number of women who are now in their thirties will never marry may be tragic for them - but frankly, it's disaster for the rest of us. Single status is now a "lifestyle" with its own TV shows, books and clever new sobriquet: "singleton". But the real issue isn't how to cope with being single, it's how to cope with singles, specifically those who are "still looking", despite a depleted market.

The moral code of the singleton is: "The end justifies the means". Under that banner, the single woman in search of love will sleep with your male friends, your exes (well, you're married now) and your brother. They break hearts without even knowing it because, in the singleton psychology, there is only one victim and that is she. The "man shortage" means they have to trawl closer to shore, and although they may be careful not to sh** on their own doorstep, they think nothing of sh***ing on yours. I lost a friend for ever when a girlfriend of mine trampled her stilettos across his emotions and his pine floors. He had asked me what she was like and I, loyal to her, assured him she was lovely. Later I questioned her; what went wrong? She merely shrugged: "Well, when I realised I was never going to marry him, I didn't see the point in continuing." Those are singleton rules.

Other singleton rules, created out of high priority need, include the licence to cancel a prior commitment with you in favour of a date - still! When you do meet up, they want to moan about their life and they want you to moan with them, only you can't because you are really perfectly happy. Off limits, too, are those funny, horrifyingly frank conversations women enjoy, because a) it would be disloyal to your husband and b) you can't bring yourself to tell her that one of the best things about being married is good sex on tap. And disappointingly, singletons don't want to talk about renovating houses instead.

Whereas single male friends have a nasty habit of fading away once you are married, single girlfriends cling on, often preferring the company of couples, in the hope of meeting a nice, carefully vetted man through you and your husband. But I find matchmaking impossible ("What on earth made you think I'd like him?") and singletons complain about being "set up". They also dislike being the only single person at a dinner and are equally resentful if they're not invited at all. Sometimes they turn up only to leave early if they don't fancy the dish of the day.

Until her next torrid romance, she will treat your home and your husband as her own. He may be used at will as her stand-by date or stand-in husband, general handyman, rescuer and confidante. She can also flirt with him whenever she pleases. I once went to lunch at a house where the single best friend described herself as the husband's "wifelet". Every time she did it, she giggled and the real wife gave a tight little smile. Sometimes this game can get a bit out of hand. "She wants my life," a married friend once confessed to me, only a trifle paranoid. "It's like The Hand That Rocks The Cradle."

When I was younger, I remember listening to an older man of my parents' generation laugh at how "jealous" women could be of each other. But this isn't plain old sexual jealousy. This is covetousness, and it seeps through your relationship like ice water. It works both ways, too. What she is, you once were and can never be again. What you have, she may never. And even though you may ultimately come to suspect that she might be secretly delighted if your relationship fell apart, in the meantime you can never admit to her, no matter how much she begs you, why you really think she is still single.