There is so much intricacy to the male/female dating,relationship and sex that some men just discover that they can pick up a guy have nsa sex, no drama and move on to the next.
A guy knows what another guy wants/needs and usually will deliver without the attachment that women requre. I never knew it could be like that, and I flourished, and he relished. As for drama, well, we have drama now, that's for damn sure.
Whether he's bi or gay or just a little bi-curious, he's obviously turned on by the idea of sex with men.
I realize that's not the answer you want, but there's about a 99% chance that it's the case.
Barbara, Well you asked a specific question and I have a specific answer for you (if you are certain that he is not gay). On the surface that might sound simplistic, but bear with me.
Guys who want sex are easy to approach by other men.
I know a woman who was married for 32 years to a man that eventually figured out he was gay.