There is so many people furious there is romance at all in the game, but let me remind you that romance is only a facet of the whole story. There is a lack of games where you can find balanced amounts of battle, politics AND romance. Some of us crave that - I certainly do. I get bored of games only focusing on battle and that have shallow writing on romance or bonding, but I also have no interest in "dating sims" because only romance is boring too.
About the polycule thing, I have more to say about Karlach since I played with her as a partner and as herself. She gets a bit confusing, because she will say for tav to go ahead and sleep with people while you can't do it with her, but then she will break up with you if you sleep with someone else later. I understand its a thing of she not wanting tav to miss on anything on her account, but there is no "transition" dialogue, no relationship discussion that clearly states now she wants you to be exclusive.
And I think she and Halsin would be a terrible idea. I see Karlach x Astarion (x tav) as a much more feasible polycule, but even then, I have concerns over Astarion himself. I find it weird he considers accepting Halsin into the relationship with tav AT ALL. I'd expect him to take it slow, and one at a time, at least for a longer while after all he's been (is going) through.
If you romance him, and after Cazador (with him as a spawn in my case), go back to the Drow twins and sleep with them, Astarion will say something like "yes, now that I'm free to figure out what I'm into. I'll run away from the room if I don't like it" or something. Then he proceeds to dissociate himself during the act nonetheless. He has no further dialogue to develop what was it happened to him afterwards (I think you might get that if you are NOT in a relationship with him?).
That is to say, I find it weird putting Astarion as just fine with a poly dynamic so soon after he is 'finding himself'. Especially because the way he laughs when you mention Halsin is into you comes across as kinda bitter. But then, there's the purposeful ambiguity there too, to allow us to headcanon a bit - which is really nice.
