I just started my first poly relationship with this guy. When we first started talking he told me straight up that he was poly and that he planned on proposing to his girlfriend of two years. It didn't bother me because I was just looking for fun and not anything serious. It's been two months, and I'm not saying I'm in love with him, but I'm kinda sad that I wont get to marry him. He's literally the perfect person and I'm sad I didn't get to him first. What do I do?
Polyamory holds that "love is not a zero-sum game," meaning that if someone gets something, it does not mean that other people can't have that. Like, if I eat a cookie, then you don't get the cookie (zero-sum). But if I am listening to a song, you can also stand near me and hear the same song, and neither of us has a diminished experience of the song.
That's how polyamory works. Including polyamorous marriage and polyamorous weddings. So the framing of "who got to him first" doesn't make sense - he's a song, not a cookie. Who knows whether in two years, you two will feel ready to commit, to live together, to share lives, to blend families, and to hold a big lavish party celebrating that?
Talk to your partner to get a feel for what engagement and marriage means for him and his other relationships - you're having fears and feelings based on your internal understanding of what relationships look like and what marriage means. You gotta get the real lay of the land rather than relying on your assumptions - that's why polyamory is all about open communication!