A: It's possible that he just told you that he was gay so you would think of him more as a girl friend and tell him more. or he's bi, like you said. if he asks you out, you should tell him that your friend likes him (if you want to tell him), deny him and hope it doesn't hurt your friendship, or... more
A: Just go up to her and say something like, "hey." just something really simple. or you could say, "you look familiar. didn't you go to my school?" or something like that. or maybe you can get one of your friends to get to know her and introduce you 2, and see where that takes you.and yes, to answer... more
A: Wait. he has a girlfriend but he grabs your butt? personally, I would stop flirting with him, and tell him that flirting might not be the best thing to do if he has a gf.