my patterns of desire and arousal were dramatically altered through experience.

Me too. Without experience, we may think we are concretely one thing, when instead we are either latent or capable of becoming another.

Some men are definitely homosexual... There are probably at least as many heterosexual men... But I no longer believe that the ability to enjoy sex with women signifies that a man is innately incapable of enjoying sex with men.

Agree there too. I'm still diving into the history of same-sex behavior, and presently have more questions than concrete answers, but, yes, it appears that there is some sort of "bisexual" phenomena in men that has existed for a while now. (That's not to say heterosexuality and homosexuality don't exist.) What exactly that is, or if there are multiple phenomena... Gay-for-pay, "actual" bisexuality, dual control model, lust on a gradient from preferred to non-preferred partners, deprivation of preferred sexed partners such as in prison, etc?

Obviously we're all physically capable of sexual pleasure and orgasm with a non-preferred sexed partner. Trying to discern lust from behavior in historical record is tough. Evolution certainly wants to point us towards heterosexuality, just look at the functional pairing of the respective genitalia, but that does not mean it's necessarily keeping us away from same-sex behavior.

It's fascinating. I get the impression that I'm working inside too narrow of a box... good fun stuff though.