But even with a straight man, you're likely to find that. Lots of straight men are happy to have one night stands or flings with women they don't see any prospect of romance or a future with. I think for most men, sexual attraction and romantic attraction are two separate things, whereas for women, they're more intertwined. (Obviously I'm generalising here, and there are plenty of people of both sexes who break the stereotype)
I think the reason for that comes down to vulnerability
I'll try and explain. I'm like the OP, in that I'm a bisexual man, but not really romantically attracted to men, only sexually.
For me, sex is the easy bit. It's fun, it's messy, its telling your body to do things to do someone else and generally its easy to work out what they like. For me, sex in the early days of a relationship is much the same whether it's with a man or a woman. Not the actions obviously, but the feelings involved.
Romance on the other hand is different. Romance involves being vulnerable with someone. It's intimate in a way sex isn't. It means letting someone else know your thoughts, feelings, fears. It means trusting someone else not to hurt you.
I'll happily roll around in bed with another man, but I can't imagine curling up in a mans lap sobbing my eyes out because my Mums died.
Women are vulnerable during sex in a way men just aren't. Yes, I could be hurt by another man during sex, but I'm 6ft 3 and built like a rugby player. If they hurt me, I can turn around and hurt them right back. So there's no risk, no vulnerability.
And I think thats why a lot of bi men are happy to have sex with other men, but want a relationship with a women. It's not because they want kids, or a heteronormative lifestyle. It's because they can't imagine themselves being intimate with a man.