have you read "i need to talk" thread?

what I can say is: at the moment you start to love a friend, two things may happen: 1st, you two get along as bf/gf, or 2nd, the friendship becomes more 'powerful'. if no one of these things happens, you could be sure that the girl isn't your best friend in the world

and went out the window cause she was your girlfriend not because she was your friend
but I must say that she must be suffering too. She may be having the same thought yours. and probably she'll get a little distant, but there's no need to worry - she needs to think about everything. You have seen that the relationship as bf/gf isn't the best way for you two, so, why you two don't try to start over the friendship again? and again: if she doesn't accept you as friend anymore (what I doubt, since you're very close friends), she does not worth your love as a friend.
of course i'm saying that imho, and I may not imagine what you're really feeling shadow, cause its easy for other person analyze the situation and give guesses. I know its easy to say all of this (and to make these things real are hard), but I really hope this can help you somehow