I consider myself pansexual, although I'll often use bisexual to describe myself as most people understand that word more. I believe I started questioning sexuality as long as 2 years ago, and in a way, never fully accepted that I was heterosexual, but just shrugged off any homosexual tendencies as just awkward moments or something. Almost as if they were normal, but you were supposed to default back to being attracted only to girls because homosexual attraction wouldn't be as good or something.
There was even a period back then when I enjoyed lots of yaoi and gay porn, and didn't even consciously think "this is gay, I'm bisexual" or anything. I found myself attracted to all kinds of genders and gender identities.
It was actually the moment where I stopped and thought "what am I?" that I felt distressed about the whole thing. For awhile, it was all just in my head, but eventually I realized that I would want to pursue these desires, talk about them, meet similar people and basically open up to a world that was sometimes, unfortunately, indifferent, non-understanding, and hateful, and the fact that it was that way made me somewhat depressed and even uncomfortable with my sexuality.
Suddenly I had to deal with labels, stereotypes, expectations on how to act, expectations on my sexuality and many other things put forth by other people, the media, society and religion. I still don't think the bisexual label fits entirely, sometimes I feel it does, sometimes not, sometimes I feel like mentally adopting other labels (even gay or straight or others) for awhile. I feel like I change orientations like personas, I get into that certain mindset for certain types of attraction.
I think sexuality matters. Not in the negative way, but in that your sexuality is a big part of who you are. I think how fluid my sexuality is, is sort of part of how fluid of a person I am. I assume and embrace many different personas, moods, beliefs, sexual orientations, and occasionally gender identities (although that's one of the harder things to explore, I've found).