>>4
This. I have been trying to tell people this for ages. If you're close friends with a member of the opposite sex, you are bound to develop "more than friend" feelings for them. Unless they are ugly as fuck, it's almost inevitable.

As for the OP, the only way to lessen your feelings for him is to stop seeing him. There's no way you can debate this. If you keep seeing him, your feelings for him will remain and probably get even stronger as time goes on.

Just...don't even do it. If he's already in a serious relationship and they are happy together as you claim, then you are screwed. It may sound difficult now but you need to move on with your life. HE'S TAKEN. You need to get over him and the only way you can do that is to stop seeing him.

So in short, pretty much what >>6 said.