What should I do? And am I doing the right thing?

Okay there is this girl that i hangout with all the time and well i kinda devoloped feelings for her and i think she has some for me....but sadly she has a boyfriend and we have talked alot about it and even made out a few times......she goes home almost every weekend (I live on a campus) and comes back looking like she went to war....idk what exactly to say or do any more its almost like she doesnt want to be friends or anything anymore we used to do alot and i would always be thinking what the hell am i doing she has someone but the emotions just seem to take control.....with her i'm calm, relaxed, not a care in the world....im just not myself....i've tried being friends with her she has kissed me on multiple accounts after I attempted to back off and I reminded her of her relationship and all she says is i treat her better than him.....Help Me please....