this one's a toughy. Help?

I'm Bisexual. No one knows. none of my friends know. to tell you the truth i'm only half sure myself. My problem is that i have a crush on one of my friends. i love her to death and i'd like to be her girlfriend. the kick ya in the crotch, spit on your neck wonderful part about it is that she has a boyfriend. i'm 99% sure she's straight. i wish i could tell her but i dont want to loose one of my best friends. what should i do?