Please help because I think I'm in love with my best friend.?

I just can't atop thinking about her and I don't have the guts to tell her I've liked her since the 6th grade, when we first met. I tried asking her out back then but she rejected and then I went out with someone else and kinda got over her and now Im in love with her again. I've always been the guy who is always there for her and I know I'm not the best looking person she could have but I just really can't stop liking her. Please tell me what you think I should do or advice. Thanks