Am I in the clear or am I a selfish whole. Just provide ur opinion.?

Ok so I have been thinking about asking this girl out but she was dateing some 1 else. I started talking to her more and as I did I liked her more and more. In any way she was telling me about her relationship and how it was n realy bad shape. I gave her some advice which she listened to and left the guy( good riddance he's a needy whole). So I figured this was perfect timing, I was stoked and couldn't wait to ask her out when I saw her next. However I was talking to a buddy of mine, who has just so happened to be crazy about her fore months, and he tells me that he's going to prom with her. He told me that she didn't want to be alone at prom and he suggested they go together and she agreed. She fliers with me pretty often and I get the feeling that a mutual friend of ours is trying to get us together. N short I know n my heart that I want to b with her and my head tells me she likes my friend as a friend only so would I b an whole for crushing my friends dreams by living my own. I have been tearing myself apart thinking about what to do.