I'm new here. But wanted to respond.
I have always known I could love more than one person at a time. When I was young it was easy and no big deal-I always had 2-3 "best friends" but at that point sex wasn't a part of my life.
When sex came into the picture things got more complicated. I've only dated one man who was ok with the idea of poly relationships (though we didn't know that word when we dated).
I have always had "someone on the side" for intimacy and most of my relationships were ok with that as long as they got the promise I wouldn't have sex with that person.
Then I got married.
The man I am married to isn't agreeable to poly relationships but knows I am madly in love with him AND my best friend. It's been a nightmare for years now trying to figure out where we draw the lines etc. At first I tried to conform, but that doesn't work well and now we're "re-negotiating" our relationship.
I think some people "knew" they were different all along-but like me just didn't know that it was OK.