Im so confused

okay so I've been talking to this guy on the phone for about 3 months. When we originally started talking, his intentions were not good, but I talked to him anyway because I thought that was all I would want from him to. but that didn't happen. We began to talk on the phone everyday for hours and we took walks together on a regular basis. He was even about to meet my mom! And I think I was falling in love with him. But then he went away to peru on vacation and when he got back he never called me. And when classes started again, I saw him back with his ex girlfriend! My friend is good friends with him and he told her that he still liked me and he wished things didn't turn out the way they did. ANd then I have two classes with this guy and now were 'cool' because I can't let it show that I still like him a lot b/c that would make me loook stupid. He apologized to me but not directly. And now were friends but he does little flirty things here and there which just make me remember what we used to have. What did I do wrong to push him away?? Anyway to make a long story short, I think I'm in love with him! Is that possible that that could happen in such a short period of time? It really hurts me when I see him and her together in school, sometimes I almost cry! I need some help am I really in love or is there a deeper problem. Please help!!

well flirt back at him just dont let his girlfriend see, and call him be friennds for now its better havin one pease of him then none for now and he will most likely turn to youif you show him you still care but tell him the rest is up to him.