So yes, as I said, if you treat Halsin's thing not as proper romance , but fling or just casual sex - it makes much more sense with all her dialogue in act 2(her denying poly proposals). She is just ok with open relationship(just like Astarion/Karlach) if Tav is ok with that, but remains mono.
I think it comes down to understanding of poly - I've read all the attempt the classify poly relationships and think it comes down to this: it's poly if the partners think it's poly.
I consider "open relationships" a type of poly. Usually used by people who want to be poly but don't want to consider themselves part of a club or who just really, really hate mashing latin and greek roots together.
