Not only do I believe bisexuality is real, but I believe everyone is bisexual to some degree. I would say I'm slightly bisexual, since I can look at two guys and tell you which one is hotter.

Nature shows bisexuality to be almost the norm, but society probably forces MOST people to pick one side or the other.

I don't claim to be bisexual, I claim to be straight, but I think "straight" and "gay" are just the two ends of the bisexuality spectrum.