I tried (long distance) dating a poly dude in a situation where he had a long term live-in boyfriend and got me and a trans girl to start dating him around the same time. He wanted a polycule to work out and it seemed plausible-ish for a few months, but the communication was atrocious. Everyone liked the central poly dude and I tried getting along with the other two, but it was clear they were just interested in the main dude. Turned into a mega jealousy situation between all of us which blew up horribly and spectacularly.
In a good monogamous relationship now, but I wouldn’t even try a poly thing again. It requires a lot of communication, moving parts, and if someone is slightly less than truthful it’s probably doomed to fail lol.