The first step is always the hardest ! so well done on posting about how you feel here!
Sexuality can be very fluid for some people ie we are neither fully gay/straight/bi. Putting a label on how you feel can make you more confused!
Only you will really know how you feel.
It took me years of confusion before I realised that I was a lesbian.
Before that I was in a long term relationship with a man, that looking back now never felt right. But I know that now because I am in a long term relationship with a woman (I knew I was gay at my first female kiss!).
When I was your age I would have loved to have had the opportunity to date a woman or at the very least talk to someone about my confusion.
If you dont feel comfortable confiding in your friend, then find an alternative, be brave and make contact with your local LGBT group (like Outhouse) and go for it! Some very nice people (who dont bite) in these groups, that will help you along your journey.
And remember you are young, have fun along the way. Oh and if the relationships you have had with guys dont turn you on, then blame the guys!!! might have nothing to do with 'self esteem' issues at all! (some guys are sh*t in bed, as are some gals lol).