i tend to think that, when you're 17, the truth will out. that age group is not really great about keeping these kind of secrets. when i was in high school a good friend of mine told me she was attracted to me, and i said that i was flattered but it wasn't going to happen, and we went on being friends. it might have been hard for her. i don't know. we're not in touch now but she's involved with women and i'm not. i had another set of friends who had something similar happen, and neither of them are gay as adults.

anyway my point is things are already awkward, at least for you, and if she's a really good friend, and you don't go too overboard in expressing your feelings, probably nothing bad will happen if you tell her. give her an out. be prepared to take no for an answer and don't freak out.

my personal experience is, your whole life you will occasionally feel attraction to your good friends, just because you're close to them, and because people are sexual. sexuality is a lot more flexible than it's sometimes presented. so you don't have to draw any huge conclusions from this.