She's not going to be dating either of you for a long time, and it would be rude to her to ask when she's still obviously (?) not ready. So the only action you can take is with your friend. You can talk it out with him, or you can just wait. That's up to you.
I mean, there's no "good" course of action here. And talking to this guy--is it appropriate? Is it necessary? If it's neither appropriate nor necessary and you both just happen to like the same girl, then there's no real need to air out all this dirty laundry. He knows you like her. Letting him know that you know that he likes her too, subtly, could help. But all-in-all, I'd say that you're in a really sticky situation you'll need time for.
I'm just saying, when I was dating last my "best friend" made a serious attempt on the guy in question and it basically led to the destruction of all 3-choose-2 = 3 relationships any of us had with each other.
But if it were me, speaking with the benefit of experience, I'd say that she turned you down and now it's your friend's turn to have a shot, especially because he apparently liked her longer than you did--and because high school dating is just a pain all around. It's really good to have a best friend. It's pretty good to have a girlfriend. But, frankly, in these politics you've already "struck out" by asking too soon, damaged your initial chance, and now if you knowingly try again it'll be hard on the girl and hard on your relationship with your friend.
Furthermore, too soon (without saying "if you asked later, I would have probably said yes," or similar) is just... kind of a nice way of saying no. If someone says no, for any reason other than "I'm busy, how about next week," then they've said no and you should probably drop it for a good long time.
So, in the end, here's my personal verdict: talk it over with your friend and let him know about what you know of the situation, but defer to him. Find a different girl, or just try to get over this one--if you hang on her while she's unavailable, it's going to be creepy and unattractive. Once you feel that you're over her and the mess between her and your friend clears up, you could try again. But right now... nah. It's just not going to work too well.
Sorry =/