edit: in response to yaason, I forgot to quote
Seriously dude, you are like 18 or 19, right?
Unless you are totally mopy or can't talk about anything else, many girls don't mind a guy who is getting over a lost love. I think they find it romantic or something stupid like that.
Sometimes they even get that "nurse the wounded animal back to health" thing going on and decide that they are the one who can 'fix' you, which can be convenient (but can also be annoying, I guess).
Start seeing other chicks. It will either a) make you find someone else, b) make the ex jealous, c) show you that what you really truly did want was what you had nad inspire you to convince her to give it another try.