I don't think that this other girl liking him should be made into an issue. A few months back, I liked this guy, but I knew that an acquaintance (with whom I shared many mutual friends) had liked him for much longer than me. She always said that it was OK that I liked him, but if I ever flirted with him you could tell that she wasn't happy about it. Because of that, I decided to do nothing about it (it would have had to have been me who made the first move, as the guy was really shy). I moved on, but just recently I found out that he liked me back when I used to like him, and I can't help feeling that was a missed opportunity, which I regret a little. Basically, you've not really got much to lose, so you might as well find out if he feels the same way.