How can I forget about this girl?

Well, this has been going on for months okay. I have liked her since late september and I have always been there for her when she has lost the twats she has wasted her time on and still, even though she knows I like her more than any other guy could like her but yet she still wastes time on heads. It's destroying me everytime she dumps a guy, I get my hopes up and then she goes and ******* gets another **** who lasts about 2 weeks. My world comes crashing down everytime she does it and I've have enough, how can I forget about her it is just killing me to like her anymore.