What can I do? Please help?

I think I like my friend she is a girl I am a girl. I don't really now what to do. I haven't felt this way before. But she gives me butterflies. We are good friends we know who each other likes and everything, and we are pretty touchy feely. She is lesbian, and she thinks i'm straight. She's the only girl i've ever liked. I have way more interest in guys. But I definitely like her. I'm just wondering what I should do? Should I approach her about it? Am I really bi or what? Someone just help me.