Hey.
I think I always realized that I was a bit
different in that I had essentially no attraction to girls when so many other people did. I didn't make too many friends when I was young, and was actually the most chummy with adults for some reason, but when I did make friends or whatever I MOSTLY felt closer to the guys. However, I really started coming to this realization about a year and a half ago when I became physically (and somewhat romantically) attracted to certain guys at school, etc.
Regarding bisexuality - No, I do not think it's a choice. Sexuality is not a rock-solid, white and black thing. There are quite a few shades of gray--most everyone leans one way or the other, but that does not mean that there isn't room for one to be attracted to the sex that they don't lean toward. I think, to varying extents, anybody COULD have certain feelings for the same and opposite sex. In other words, I think any straight person could possibly have feelings for the same sex at some point, and vice versa. So when it comes down to it, the label is really up to your own interpretation--only YOU can decide whether to classify yourself, and if so, what classification you fit in.