I hope this doesn't go the "Poly person is proved wrong and magically becomes monogamous upon meeting the 'right' person" route because that's just insulting.
I don't mean to be "that guy", but outside of fiction, polyamorous relationships are never long-lived and are always doomed to fail. They are inherently unhealthy. Monogamous relationships are complicated enough already. The more individuals with different ways-of-thinking and motivations you throw into the mix, the more complicated and unstable the dynamic becomes. It's all in the math.