Speaking as an admittedly monogamous person (and happy with it), I have never seen a polyamorous relationship that actually worked long-term. Oh, you hear about them. Every third relationship-oriented online article seems to be in favor of them, for a variety of interesting philosophical reasons. And every once in a while you hear about a friend’s cousin’s uncle who’s been in a successful poly relationship.
But I’ve never actually seen one. I see a lot of people who think they’re in a relationship when they are, in fact, just having sex with several people, but I’ve never seen an actual, factual, stable long-term poly relationship. They seem to end in breakups or divorces. I’m starting to think there’s a reason why.