Deciding or declaring your sexuality at 15 is probably too early. I know people in their 40s who are still unsure and coming to terms with their own sexuality.

I don't even know if sexuality is concrete for everybody. Why wouldn't sexual desire change as we grow older? Our bodies change, our self-image changes, hormones and drives change. Others have said it - I'll say it again; don't worry about labels. Having a name for it and a set of "rules" doesn't always make living that way any easier.

Your reactions to your female friends? Totes normal. I'm too self-conscious to dance, but as I understand it dance can be very freeing. Add some drinks, and almost anything could happen.

Feeling protective of friends is more of a macho stereotype than anything sexual. You've grown up with testosterone in your body, and a lot of social pressure to be 'manly'.

Take my words with a grain of salt. I'm an old fashioned guy, (48/m) raised in a big family where Archie Bunker had moderate opinions on race and sexuality. I've learned to be more rational and compassionate - and to accept that not everybody fits into traditional neatly-defined roles. Intellectually I'm sex-positive and trying to overcome my own prejudices.

It is relatively 'normal' for a hetero guy/gal to have some homosexual experiences, even though this would violate social norms. Experimentation with sexuality is okay, as long as nobody gets hurt. I'd think it would be easier, at least socially for someone who is (mostly) homosexual to experiment with traditional heterosexuality.

TL;DR - I didn't really know if I wanted to be a fireman, engineer, actor or writer when I was 19. Those are jobs we can always quit and try something new. Making a declaration of sexuality, especially since you mention possible transitions is a lot more permanent. Stop pressuring yourself to fit into a mold, and enjoy the exploration. Just respect yourself and the people you interact with.