In love with my best friend?

So, there's this girl. We are best friends and have been for over a year now. We are really close and talk about everything. Recently, she's been talking a lot about how we should just go out because we are so close to each other. I know that if we went out we would be able to hang out more and get physically closer to each other. I just don't know though. The main reason I don't want to go out with her is because I don't want it to end up destroying our friendship. I love her a lot and she says the same about me. The main problem that I have with her is that she has been fingered by other guys in the past who she wasn't going out with and a lot of people think she is a slut. I don't care what people say, but I think they are right. She constantly flirts with every guy she sees even if she says she doesn't like them, especially guys that are a lot older than her. I confronted her about this and it just ended up in tears and her saying shes changed, even though I know she hasn't. Its not a major issue, but I don't want to go out with a girl who will constantly flirt with other guys. I don't think its her fault, but I just don't think I can handle it all. Now, I find it hard to continue to be best friends with her because I end up developing feelings for her and I know I can't go out with her so it just hurts more cause I know she likes so many different guys. I still want to be best friends with her, but don't to have feelings for someone who is like that. I just wish she wasn't. What should I do?