over a year ago:
hi i was in a really similar situation just a few months ago. so i know kinda how you feel.
what happened to me is that i was in 10th grade, he was my best friend in 11th grade but i didn't have the courage to tell him exactly how i felt. my other so called 'friend', realised this and she pretended to me she was trying to help me to tell him, and i thought this was really kind of her so i let her intervene. to cut a long story short instead of helping me she helped herself. it turned out that she liked him too and she couldn't tell him either, but when i came along she realised she had to. i was set up. and now he is with her and i can't say anything. besides, they've left high school now because they were both in 11th grade and i was only in 10th, and gone to the same college. she was such a stalker she changed colleges when he did.
i know its a bit different from your situation, but i still might be able 2 help. :-)
to help you out with your problem, this is what i'd advise you to do:
first of all, get help from your brother or sister, or your friends if you can trust them. you have to explain all what you've said here cos i don't think this is one you can get out of on your own without advise.
because the guy you like is your best mate, you might be able to talk about it. maybe start the conversation really carefully, and make sure you're alone. maybe squirt your eyes with water first so it looks like you've been crying cos he's more likely to be more understanding. [but dont over do it]. then you should talk for a while.
if you don't want to talk to the guy, then you could try thinking of a way to get "her" out of the picture. this involves a lot of planning and careful thought. but the fact that it's a little bit mean doesn't matter if she's a bitch like you said.
what ever you decide to do, what you have to remember is: to act like you fancy him when HE's around, but act like you totally don't when SHE's around. that way she wont know what you think or what you plan to do, but HE will begin to realise that maybe he's made a big mistake going out with this bitch.
but, whatever you decide to do, good luck lol ;-D