questioning

What is it that attracts us to emotionally unavailable people?

Last week, Tuesday night perhaps, KT and I ran into E in the pub having drinks for a friends birthday. He and I snuck aside for a bit to have a "talk". I was aware this talk was coming, had thought extensively about what I wanted to saw, and was glad to run into him so we could get it out of the way. He said that he had been worried that he was taking advantage of me and giving a false impression about his situation, which is in fact thus - he is still in emotional turmoil from being dumped by the love of his life a month or two ago and was, in effect, still in love with her. I explained that I was fully aware of this situation and did not have any expectations on him. We did the whole "whatever happens, we should still be able to be friends" thing, which he qualified with that he hoped we could still have a cheeky snog now and then, I said he could stay over whenever. Typical - that night, having gotten everything out in the open, and gotten very drunks, went back to mine for a shag.

Now I'm back to vacillating between thinking this is a fine and fun situation, to thinking "what do I think I'm doing?" Certainly not in a bad way - just fleeting thoughts that don't particularly give me much bother, but I do wonder whether I'm setting myself up for failure so to speak.
The problem is that I can't seem to stop fancying him at the moment - is it the unavailability? or is it very simply him?

I think its a combination of the two.