The roles of Victim, Persecutor and Rescuer are linked, and sometimes intricately interchangeable in our psyches. I've been playing all three roles over the past few months, in an Internet exchange with a brilliant, if perhaps sadistic, young fantasist, that has left me puzzling over the nature of depression and paranoia.

In my depression over the summer, I was all too ready to believe that the world was a sinister place, that there were corrupt and amoral souls out to exploit vulnerable kids. (I am well aware that this is objectively true no matter what my mood - but we all manage some way to anaesthetise ourselves from the horror of the daily news, otherwise we'd never manage to get out of bed. My point is that I lost that anaesthetic capacity.)

My inner world, dark and troubling, sought reflection in outer reality. By engaging in a mission of rescue, of at least two young men whom I was led to believe were being blackmailed and exploited, I was somehow trying to externalise and resolve my struggle. My knowledge that the urge to rescue hides a deeper need to be rescued was remembered - but when depression takes over, all sorts of sensible things are forgotten.

The young man who obligingly co-created my nemesis intimated, in our last conversation, when he finally introduced himself and admitted that it was all a Mephistophelian masquerade, that he knows a very good libel lawyer - so I won't say who he is. It's irrelevant for the purposes of this column.

An explanation is necessary for those who are not familiar with the Internet. The forum for my exchanges with him was an anonymous chatroom for gay men. People identify themselves with a nick(name) and a short sentence describing themselves and what they're into. There is absolutely no way of establishing whether you are talking to someone genuine or not - in these chatrooms, fantasy rules.

I first made contact with Nick (as good a name as any) about a year or two ago. We started off in fantasy mode, and then he got honest, introducing himself, and talked about how weird it was to have such wild sexual fantasies as those we were discussing, and how troubling they can be if one has a public image of being Mr Nice Guy, Mr Boy-next-door. We had a nice human friendly chat and that was it.

A few months ago, a character appeared called "horny fucker" whose intro said that he was "into using young lads and chatting to others into the same".

I started chatting with him, playing him along, to see how serious he was; and he was open to being questioned. He said he was 32, bragged about his exploits, how he found young closeted guys with low self-esteem and turned them on - then blackmailed them, then fucked them bareback - and he "confessed" to being HIV positive.

He revelled in his hedonism, railed against my moralising and prudishness, and gave voice to that part of me that one has to suppress to survive - the part that craves reckless abandonment, to shrug off the tyranny of latex and guilt and fear and dive into pure unadulterated selfish pleasure.

In fantasy mode, I gave as good as I got - revealing a hell of a lot of my own psyche in the process, which proved to be rich material for Nick to use against me over the coming months.

He then staged a brilliant piece of theatre for me. In these chatrooms, you can be more than one person. One afternoon, he simultaneously played the Exploiter as well as a young well-known closeted actor, falling for his devilish charms. I fell for it, hook, line and sinker.

It was highly disturbing for me. It was painful to "witness" a young lad apparently succumb to the lure of reckless unsafe SM sex - and I've met enough young men who don't care about being infected to support my fear, and to believe it was true. I even went to watch the actor in a show a few days later, and dropped a note afterwards to him backstage - thankfully vague and including a disclaimer paragraph saying someone may have been pretending to be him, and apologising if that was the case. Not surprisingly, he never got back to me. I must have seemed mad. Perhaps I was.

Then the battle really began. I began adopting as many different identities as I could think of to engage the Exploiter in conversation - and I began to get a feel for when I was chatting to the same guy, for he, too, adopted different identities constantly. On the net, grammar and speed of typing and attitude are the clues to personality. Many many times we chatted under various guises - some of mine he guessed, some of his I guessed, and I imagine that many times neither of us clicked it was each other.

At all times, however, I was playing around with this concept of the interchangeable role of victim/persecutor/rescuer - in trying to figure it out, and track this man down, I realised that I could be the victim of one man's fantasies, as well as his persecutor trying to bring him to book, as well as the rescuer, trying to save his soul. I even took legal advice on the law of blackmail, and wrote to his more accessible and more frequently mentioned abused young "slave" - Nick himself. But Nick replied coyly, or not at all, leading me to believe he was frightened.

When Nick revealed to me that the game was over, I was relieved and strangely satisfied. As was he. I had told him the week previously that it had occurred to me that the Exploiter was Nick himself, and that it was an amusing thought. Once I'd cottoned on, it was only a matter of time before the dramatic tension began to wane, and the cat & mouse game ceased to be fun for him.

Now that it's over, I realise that I've been hurt by all this. He was terribly cruel in attacking my morality and my pretensions to rise above amoral hedonism, ridiculing my "prissiness" and my determination to stick to the uncomfortable position of ambivalence about the toxic pleasure of untrammelled desire. His mocking was hard to bear - and the glee with which he described the miserable state that "Nick" was in was so hard to stomach.

It is no surprise that within days of the Prozac kicking in, and the depression started to lift (although I'm not out of the woods yet) my external reality should also shift, with Nick admitting to having created his own fictional abuser, and that, far from being miserable and trapped in an abusive hateful situation, he was in a good monogamous relationship, and that I had never chatted to the actor. His only complaint was that he was bored with himself - and with a mind as perverse and creative as his, I can quite see why.

As my internal demons become subdued for a while, and I find some peace, so my external reality changes - and I no longer have a nemesis against whom I can feel righteous, no suffering victims who need to be rescued.

I'm thrown back to a sadder and wiser state of being; the realisation that sex and life is always far more subtle and complex - and less black-and-white - than the cruel seductive certainties of erotic fantasy.