Well being with your best friend can make or break that friendship, seems to me like you need to talk to her about how you feel and see how she feels about you. The outcome can be one of two. One she might like you back and who knows you might end up together in a relationship. The second, you tell her and she doesn't feel the same or doesn't want a relationship with her best friend which might cause things to be awkward at times however your friendship can survive this.
Another thing you have to think about is if you were together were you to break up you might end up losing your friendship as this can happen. It's all about whether you feel it's the right thing for you to do and only you can make that decision.
I have seen two best friends get together before and they are still together after two years and are still very much in love, so there is the success stories that you hear about. Good luck in whatever choice you decide to make.
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