Stop trying to classify yourself as straight, lesbian, or bisexual.  Start trying to figure it out, instead.  When you're young, and your sexual side is just being awakened, is it really surprising that you might be attracted to things you've never noticed before, or that you might begin to question certain aspects of your sexuality?

Of course it isn't.  A lot of information starts coming your way, and your hormones just complicate the entire situation.  Let things develop on their own.  Don't force them, don't complicate them, just go through the motions.  You'll get your answer as time goes on, but you don't want to ruin a friendship, as you said.

You also have to protect certain things.  As much as I hate to say it, sometimes our friends aren't as understanding as we wished they were, and sometimes they aren't as trustworthy as we wished they were.  You also have to consider how society would treat you, sadly.  You don't need to open yourself up to those kinds of troubles, until you are confident in yourself, and ready for what may come.

1/4 of your life is spent being a kid.  Why not spend that 1/4 being a kid and growing, then dedicate the 3/4 of it to classifying yourself if that's still what you're interested in doing?  All of these questions will be answered, but to be honest, life is a bit too complicated for a teenager to accurately determine some things, and sexuality is one of them.