What do I do if I'm falling for my best friend?

Ok so I am 15 and I do know that we're young and all that, but that doesn't change the fact that we still fall in love. We've been close friends for a while and I mean we are really close and lately I've developed feelings for her and at first I just ignored them because I though it was just because we are so close, but I'm sure it's not that anymore and I don't want to ruin our friendship, but I don't know what to do.