OP, you have to KILL your romantic feelings for her.
Speaking as a bi girl, if she were into you, she would have responded positively by now. You have more or less confessed to her your feelings on more than one occasion, and she only responds by pushing you away, right? It's the same in any best-friend type relationship, gay or straight, when one of them develops unrequited feelings for the other...the more you like her and try to push her into something, the more she will be uncomfortable and try to push away.
If you want to keep your friendship, you really have to give up on your feelings for her, no matter how intense they may be. If you don't think you can handle that, or if it'll just make you fight more, then you have to go with >>5's route and break off all contact. It isn't healthy and will only end badly.
I've been there, with best friends, before. it was difficult getting over my feelings, and very painful, but I told them, "I like you, but I'm trying to get over you, please be patient with me" and I'd just try to be as non-sketchy and platonic as possible. 9Keep cuddling and hand-holding to a minimum, obvs, haha) we worked it through and although it took a long time, in the end we were even closer than before, as long as I resigned myself to thinking about them only platonically.
When you really, really like a person it seems like there will never be anyone else, especially if it's the first person you feel that way about, but you know, you eventually do move on and find other people. Hopefully she cares about you and will be understanding, but if not - think about it, do you want to hurt now for a while and then move on with your life, or do you want to spend another four years in painful limbo, chasing after something that you can't have?