I only knew one Poly couple personally and that one was a hot mess.

What used to be a lovely couple (of three years) suddenly became the boyfriend, the girlfriend and her four other boyfriends.

The power dynamic was FUBAR from what I have seen and the only reason he remained for a little bit is because he still loved her and was afraid of losing her and she knew and abused that knowledge.

Me seeing this whole thing happening in front of my eyes pretty much broke the friendship that I had with that woman.

I really do not care if people have that kind of relationship but you should make sure (from the beginning) that you are on the same page, and if you notice that your partner is not comfortable with it then have the decency to break up instead of wanting the cake and eating it too just because you are selfish.