How do prostitutes and porn workers get it up?
Simple Biology. If you physically stimulate someone's sex organs, guess what happens? They get sexually aroused.
How do you think orgasms during sexual abuse occurs? Sexual orientation doesn't preclude rape, sexual abuse, fantasies, sexual curiosity, one night stands, prostitution, drunken sexual liaisons etc etc.
Sexual orientations does NOT speak of one's sexual behavior. This was explained pages ago.
People who study sexuality go out of their way not to label specific sexual behaviors as either heterosexual or homosexual or even bisexual. They use terms like 'Men who have sex with men" or "Men who have sex with women" instead.
Sexual activity does NOT require one to be sexually attracted to their partner. See above.
Liking brunettes is not a bloody orientation, it's a personal preference. Like if one happens to like big butts (and cannot lie. Sorry had to say it.) or small breasts. Everyone, gay straight or otherwise has their own personal preferences of what they look for in a potential mate. This can be attributed to a Biological Phenomenon known as Sexual Selection pressures. Though I ain't a Biologist so don't quote me on that.