To borrow a phrase once used by someone I know: I knew I was heterosexual at a very early age. From as early as I can remember, I was powerfully attracted to the opposite sex. It was silly, really. (Isn't it, always?)
Ask any man, and he will agree: sometimes, you felt like Curly from The Three Stooges in the episode in which he was conditioned to a Pavlovian response to a bell: ding, and he started boxing. Except, for us, a pretty girl was the bell and you couldn't just start...uh...boxing. So, then, you were the cowboy from the old movies jumping out onto the team of horses to the stagecoach to stop the whole thing before it fell off of the cliff.