I dated my bestfriend of 4 years for about.. a month? We no longer talk. It sucks but dating is what ruined everything we have.
but I can honestly say that since then I have been in a relationship with my fiancee for 2 years now and we started off HATING eachother because he broke my friends heart, I'm really not sure how we came to terms but we ended up being really close friends, I was starting to fall for him without knowing it, his friend leaked info to me about him liking me. I told myself I wouldn't do it but if I didn't I would be as happy as I am now.
You're young, my advice, wait till your older to start dating bestfriends. At 13 both your hormones are cruising around, she may be the one, she may not be the one. I say keep it simple as friends, let HER come to you.