Recently our 17-year-old daughter introduced her boyfriend to us over dinner. He came with another girl which we initially thought was a common friend. No, that was actually his other girlfriend. Super nice girl, very pretty. That dinner was awkward to say the least. My husband already doesn’t like him due to this whole poly thing. I just don’t understand how our daughter could be okay with this, no matter how good the guy may be.
There’s nothing inherently wrong with poly relationships, so long as everyone is equal and respected. The thing that worries me is that you said “his other girlfriend” and not “her girlfriend.” It’s not necessarily a red flag, but it is something to be cautious of.