I have always, always, since the age of about ten years old, liked more than one person at the same time. I used to wonder, when I wrote on the back of my notebooks "I <3 Dave & I <3 Ken" if when writing two people's names, each somehow negated the other. It didn't FEEL like it, but no one else seemed to do it. I made my way through my teens in tumultuous relationships, often in love with more than one guy, and I used to (accidentally) torture them by breaking up with one to be with the other, then breaking up with that one to be with the first one. In my mind, it was the only ethical solution to avoid cheating but still get to be with them both. When I realized the pain I was causing, I later switched to just cheating. I didn't know there was another way.
I don't think I actually knew anything about alternative relationship formats until I was about 22 and dating a much older guy (37) who was really into group sex. He had all sorts of friends who were various in forms of open relationships, from just into threesomes, to into full swinging, to a couple that ended up taking on a long-term girlfriend. At the time, I harbored a lot of resentment, because his obsession with group sex (and having his head up his ass) led him to push me very hard to do things that I wasn't ready for. In the end, he let me date around while still with him, and when I fell for someone else, who was nicer to me, and stopped putting him first, we broke up.
After that, I kind of underwent a backlash for a few years, and—much the way a lot of closeted and in-denial gay people will pretend to be homophobic—I detested the idea of non-monogamy. When my ex-husband, Moss, casually dropped in an early conversation the idea that he's not sure that humans are meant to be monogamous, I flipped out on him and we had a huge fight. Later, when I was 27 and we were moving out of town and I cheated on him in a drunken moment of wanting to be so close just one more time to a really good friend, I suddenly had to revise my viewpoint. I've been musing over poly ever since, with about 10 months' total experience in actual poly relationships.
The funny part is that, in hindsight, I think my late father, who was pagan, may also have been poly and closeted to us kids. I have a half-brother who was raised in another state, who is the child of my parents' "roommate" when I was a baby. He's less than a year younger than me, and family-like pictures exist of my father in the middle with the "roommate" on one side and my mother on the other, while I am a baby and the "roommate" would have been pregnant (though not visibly) at the time.
I do know that throughout my childhood, my father had a very hard time being faithful (eventually he and my mother divorced, and he married the woman he was having an affair with), and in my late teens, he and my stepmother had a female couple over allllllll the time, even present at all holiday family dinners, and he made a point of our getting to know them, and they took a great interest in us kids. At the time, I assumed they were just really close friends with a lesbian couple, but looking back, I wonder if the four of them weren't all in a relationship together.
I can never ask him about it, though, because he died in 2005. I know such questions would be unwelcome to my mother (she's a born-again Christian now and disapproves of EVERYTHING) and probably to my stepmother too (she and I were never close, and she remarried less than a year after my father's death). It's all just speculation. Maybe I'm looking at the whole thing through too poly a lens. I will say that, if he was, it would have saved me a universe of hurt and mis-steps if I'd known such things were possible from an early age, and had had open role models to follow, rather than trying to cram myself into the box of monogamy, since it's the only thing I knew existed.