When I was in your situation I waited until the time was really right then I asked her. But I told her I needed to confide something in her and that I needed her strict confidence not to say anything to anyone no matter what. Then I told her I hoped we could still be friends after I told her. I was real scared and nervous. We had also been drinking a little bit. I told her I desired to have her. Turns out she was hot for me to. We spent a couple of nights together however we just didn't feel right about it and decided we liked boys better. Then we decided we were just curious and not really bi and decided to end it. No matter how you approach this you are risking a lot. Make sure you are private about this until you know for sure if you are or are not bi and then after you know if you are or not then decide if you want to go public with it. Generally high school is not the time to go public about such things. Kids can be real mean.
Just to let you know I just had a friend commit suicide last Thursday and he got beat up real bad at his new high school by some football players calling him gay and stuff. People say he admitted to being bi but that still may not be true..my point is you need to trust this person more than anything to let her know..cause it could always be turns out its a one time deal and this other person might go tell the world which could completely ruin your high school career..its really hard dealing with this..i know my friend didnt kill himself only because of the pressures from school..other issues involved but i wonder whether the kids beating him up had anything to do with it..he was only a sophmore...
As much as I agree with the whole "kids can be mean" thing, and it could very well be that it's merely a sexual desire, not a preferance.. Being bisexual or gay isn't something to be ashamed of and if you find that someday, you really know.. You shouldn't feel like you're alone or unable to tell anyone.. Granted, some people you shouldn't tell. I myself have been "bisexual" (or as my mother puts it, I can't make up my darn mind) for awhile now. I experiance the same feelings with my best friend when I was 14 and realized that it's just who I am..which turned out best for me. When I knew of myself, I also knew who I could tell or not tell.
Well if being bi with a girl is as unappealing from a girls point of view as 2 guys "together", then you should be very careful if you decide to tell anyone, things spread like wildfire and they are right, kids can be mean.
Ah I remember those days lol... I am Bi of course. I first tried it when I was 13... young I know.. anyways try it... if you like it stick to it if not you will know you tried something that most people dont have the courage to.