This sounds just like my wife and her best friend.
JUST like them. You're not in the mititary are you?
I had her read this and she even thought it sounded like them. She said if she had the chance she would go for it. She would just be sure to discuss it first and if either one of them thought there would be problems they would not go through with it.
Well I'm glad to report that nothing happened with me and my best friend, Sorry guys!
We went out and had a great time, she did talk about it a few times during the night, but by the time we got back to her house at 4 am she was so drunk that she just passed out.
It's probably a good thing to keep it as a platonic (you can still flirt without acting on it) relationship since you are best friends. I have a few girlfriends that I've messed around with (or still do) and luckily our relationships haven't changed but we're all a lot older than you. I have another friend and all we do is flirt and talk, but we haven't done anything physical and I think we're gonna keep it that way.
If you're bi-curious and want to explore, do it with someone who's relationship isn't as tight as it is with your best friend. This way if things get weird you won't loose someone important.