Being there for a crush

I like listening to people's stories. I love getting a glimpse of how others see the world. So, I talk to people, ask all sorts of questions and generally get everyone to open up to me relatively easy.

So, recently, I got talking with this cute guy (the thread title says "crush", but he's not; not yet anyway). He opened up completely and in just a few days he ended up talking about this girl we both know and he's got a crush on. She's not interested, but she enjoys attention and teases him.. in any case, it ended pretty much predictably: I was a shoulder to cry on, I was trying to help him, I was listening to him.. and while I liked the idea that he trusted me enough to share his feelings and secrets, it left me horribly tired. I know I couldn't ever have a shot with him, but the simple fact that I was helping him resolve his straight romance problems was almost too hard to bear.

I like people.. I like helping.. but combine getting crushes on straight guys with having people open up to me and it feels as if I always end up making sure my crushes can be happy without me. Which is a horrible thing to think that I resent; I don't, I really want them to be as happy as possible. It's just that it's so many times that the same happens. It happened several times just in the last couple of months.

What to do? This seems as something that should be a universal problem for gay people. How do you deal with friends' heterosexuality? How much does it hurt you to see people you like in the fullness of their straightness?