What should i do?

I've liked this girl for about 3 years now and she has a boyfriend and they seem to be happy together but i'm miserible cause i love her and she is affecting my whole life even though i'm not with her like i'm a really good golfer and i have a chance to be REALLY good and maybe get a scholership to college and possibly have a career in golf but right now i have no confidence and i feel horrible and so unloved, i've tried to forget about her and move on but it doesn't work i've even tried liking other girls but that dosen't work either. i need to get on with my life but i can't get over her, also her boyfriend is really cool and popular and all the girls like him and i'm somewhat popular but not like him, i think she is the most beautiful girl in the world and care about her so much. i feel like the world is ending, its so painful. I don't know why i care so much about her when i'm not even with her, i can't even pick a college to go to cause i wanna go where she goes. i'm confuesed!