Well, it seems to me you are poly... there are people who are in poly relationships with a limited amount of partners, it's called polyfidelity, although it's not exactly the same as it's not gender-based.
But I've known other people who said they were similar to you. I guess you're biamorous? Like polyamorous, but specifically two partners, one of each gender?
I don't think using labels is essential, but if you feel you need one, that's the one I have for you
. It might also be easier for you to explain to people how you work, since you work in similar ways to a monogamous person, multiplied for each gender. And a lot of people seem to understand how a male partner and a female partner would be two different things.
To find a partner, I can't help you much, I've never been too good at it. But if you do find a date, say you're poly-bi (bipoly?) and that you have a boyfriend, and that you don't expect the relationship with her to be just sex, you want an actual relationship.
If it scares her off, rince and repeat. When you meet one who isn't scared off by it, you get the chance to give it a shot