Do you know what, your 15. You really have more important things to think about. When I was 15, I thought boys would make me happy and that I should be dating. After my GCSE's/A Levels and going to college, I was happy not be thinking about boys!
Why not just have a laugh with your mates and forget about sextuality, things will turn out the way they are meant to. I know it bothers you, but while you are fretting over it, those people probably don't think about it themselves! You'r waisting you energy thinking about other people! ;-)