I know how you feel.... I used to have a very strong crush on a female teacher of mine who tutored me at my house... I was totally conviced that I was in love with her, and maybe it was even real love....I'm still not sure even after all those years.
She was very beautiful in her own way, even if she was kind of very tomboyish... in fact she was mistakened for a male sometimes (which I found hiralious, as seeing I always knew that she was a female)... and she had a killer sense of humor, which I liked.
but then I found out that she was to be enaged to some guy, which just about killed and crushed me, espeically as I was about to reveal to her that I liked her in that way... just to see where it would had gone. 
oh well, at least on the bright side, your situation is better than mine was... at least it's a best friend and not some teacher.... and who knows, maybe she's at least bi-curious? it sounds like she might be, from your descriptions of her.... so maybe you have a chance with her, even if there's a chance that she might be totally straight after all.
I go with the idea of taking her to a gay/lebsian bar "Just for kicks" to see what goes down just for fun... see how she reacts.
