I wanted to put a horse's head in your bed: An ex-wife tells her husband's new girlfriend: I hate you but he's all yours

You know, I met you once on a restaurant outing with some of his colleagues, before he and I separated, unaware of the part you were going to play in my life. You seemed nice enough, though I did notice your frizzy hair and wondered how you managed to get a comb through it. I can't go back to that restaurant or even that street now because of the hatred that any connection with you stirs up.

It's totally irrational. You were not the cause of our break-up. Years ago I had decided that the time must come when I could no longer live in a marriage where non-communication was the norm and support for each other's interests and endeavours was gradually crumbling away.

So, please, don't flatter yourself that he left me for you. I left him, walking out of our home of 25 years and he no doubt found you eager to jump into the breach.

Now you are in my house. And it is still mine in spirit, even though I'm living elsewhere. I made it, over many years, a home for my family. I decorated every room, painted every wooden surface, laid carpets, put up shelves and, despite the deterioration of the relationship, for a lot of the time it was a happy home for our children. I resent your being there; I didn't make it for you. Above all, I loathe your being in the sun-room and in the garden, both of which I designed, created and filled with plants.

You can't know the hours I have spent hating you and wondering how I can hurt you, one part of me carrying out my work and another seething with venom. However, him you are welcome to. I do hope that you are now beginning to discover some of his more unpleasant sides. At work - the Jekyll side you saw - he was amusing, hard-working, popular. But at the end of the week he had nothing left to give his family and the Hyde side was sour and uncommunicative.

The children, when small, were an irritating distraction from the work he always brought home and so had to be kept quiet or taken out. Oh, those many afternoons, rain or shine, spent in the park and playground. Housework, which I left till weekends once I had gone back to work, he absolved himself from by denying that it was necessary; he always was something of a slob.

And, of course, there were the headaches. Amazingly, they only ever occurred at weekends - and then what better reason could there be for not engaging with the children, helping in the house, going out or having friends over? Has that changed, I wonder? Perhaps you are still at the stage of being sympathetic and concerned, as I was initially. You'll find out.

Also, have you managed to address the question of personal hygiene? Tricky, this one. Growing up, his family rule was one bath a week, done very thoroughly because it had to last, and he's never seen any reason to change. This is a subject that, if a wife doesn't bring it up, not many other people will, but whenever I tried to discuss it he said he didn't believe me and no one else had ever mentioned it. Perhaps he thought I was making it all up as a snide form of attack.

Neither of you know it, but I did once go back to the house. There are still things of mine there, but I don't want them. Everything has been contaminated by proximity to you. I went upstairs and saw two pillows back on the bed, my bed, with your perfumes and powders nearby. I considered putting something in the bed, a horse's head perhaps or, better still, interleaving the tissues in the Kleenex box with itching powder. I thought about coming back at night and pouring tar over your hair (it really would be difficult to comb then), or taking a photograph of you both, at a moment of maximum embarrassment, and making dozens of photocopies to distribute around the work car park.

I wondered about leaving a few fish in a place where you'd never find them, to decompose slowly. Or I could make it look as though the house had been broken into by particularly destructive vandals, and pull everything out of drawers, tear up documents, throw paint at the walls and crack every window pane. But all I did do was pour hydrochloric acid into the plants which you had brought in, as a metaphor for what I would like to do to you.

I shall never do any of these other things. First, I cannot bear to ever go back into the house again. It is so deeply imbued with memories. Acts of destruction would be far more damaging to me than you. It's not the house and the former life it encapsulates that I want to hurt, it's you for taking my place in it.

Could you ever understand my feelings? I don't expect that you think much about those. I can imagine the sense of relief you must have that at last you've found the haven of a new partner. (Though please don't expect that he'll be a new father to your children - I think you'll know by now that he was never much of a one to his own.)

The civilised thing to say would be: 'My relationship is over. It was necessary to end it and I wish my former partner happiness.' The words are here in front of me, but I can't feel them. Not while you are present in what used to be my home.

This letter was written as an exercise at a divorce recovery group.