My best friend is a girl. I think I'm in love with her but she has a boyfriend. Right now I am her best friend and she is my best friend. Her boyfriend is one of my good friends too but both of them fight all the time. Couple days ago she stayed up with some other guy which wasn't me or her boyfriend.

Right now I guess I just care about her as a best friend. I never want to lose her as my best friend and I don't want to lose my position as her best friend. I really wouldn't know what to do if that happens. I care about her so much and would sacrifice anything for her. She means so much to me because right now she is one of the few people that actually care about me. She's always there for me and I'm always there for her too but it feels like I'm going to lose this connection. I really don't know what to do

I would tell her how you feel. You won't ever know if she feels the same, unless you talk to her about it. But let her know that you don't want to lose her friendship. If she feels pressured, don't push it. At least you will know her answer, either way. Keep trying to be there for her in any way that you can, and she will be grateful, I'm sure :)