I'm gonna give everyone here my 2 coppers, though I reckon this might be a controversial take on the situation.
I think his polyamorous shtick was shoehorned into this game for fanservice. It's phony and feels empty, without purpose. It's meant to be a fun diversion while you focus on the "real" romances (Astarion etc.) Mind you, not a fun diversion for your Tav, but for the player.
Halsin is not real and doesn't have feelings. Yet the people who he is supposed to represent are. And they (as far as I've read) are not happy with how this is handled. C'mon, a 350 year old big boy elf who can't say the word "relationship" because the term is too civilised... thanks, but no thanks.
I would have wished for him to be a run-of-the-mill mono romance, and this is the core of my opinion.
No idea why they decided to put multiple tropes and kinks into one character while forcing others to participate even though it also makes 0 sense for them (literally everyone you can involve in a poly relationship either has trauma, or it goes against who they are as a person.)
I understand others might not feel the same, but this is my viewpoint of the situation and I'm glad we have a forum where we can discuss such topics and hope for feedback from Larian.