No no no...you must be 23-24!
Whoops, sorry. No matter how much I try to squelch the bitterness, it keeps coming back out.
I don't think I'm in a position where I could tell you what to do, given that I recently got out of a long relationship and have also dealt with feelings for a guy friend. I think what you/she need to figure out is what kind of feelings does she have for this guy? Is it just some run-of-the-mill crush or what? Does she have "grass is greener" syndrome?
Furthermore, I'll ask what so many people asked me...is this your first major relationship? Is it hers? Apparently this causes problems. Ack, again with the bitterness!
I'm sure if you told her you thought you were developing feelings for another girl she'd freak. I hope she's considered how this news must make you feel.