I was the same for also 4 years lol.
But then I decided to tell her and even tho I knew her answer ("no i'm straight") I just wanted her to know, cause even though I loved her, I also loved her and apreciated her very much as a friend so, after some weeks, we finally have a very strong friendship for that :D
Tho I totally get it's really does hurts, like torture everyday, sometimes not being able to think nothing but her, it's a torture :')
but honestly if it's not gonna happen just move on, it's not a good thing for neither of you specially for you, there's plenty more girls you could meet or just love yourself.
(Sorry for all the losg text, and thanks if you did read it :D)
Khm... It's veeeeery realistic. I guess everyone of us, les girls, had at least one unrequited love for straight girl. It's painful everytime...