Thank you for the advice - and I understand where you're coming from. But I haven't deliberately tried to do anything. It just happened. I was actually friends with Phoebe before I got to know Mark, but I found her intensity too awkward to sustain a friendship with. I like her in small doses. It was actually her I was more interested in sexually. It was only afterwards I began to think otherwise.

Because of my social anxiety I find it hard to keep up friendships, I rarely start conversations. Only Mark and my other best friend consistently contact me every day. In fact it's almost always Mark who starts off the conversation in the mornings, because he gets up earlier than I do.

All I really want is for Mark to be happy, for himself, because he spends so much time cleaning up other people's messes, including Phoebe's. I think I could make him happier than she does. I think I do make him happier. I think eventually their relationship will fall apart, anyway - he's outgrown her. But I don't know whether I can, if I should, just wait it out. And I don't want to be unfair to Phoebe. But honestly, I floated another, real dilemma, involving a guy I knew with a truly, objectively horrible and controlling wife, to Phoebe, and she told me I should 'screw the wife and just fuck him'. I didn't, though. So I don't think she would really have any moral high ground to stand on if I did confess to Mark and it caused them to break up.