BG3 is supposed to have this very evolved form of romances. There is put a lot of effort into to marketing this. Most are healthy ideals; support them in their goals, be respectful when challenging their beliefs, respect their agency.
But then when you reach act three for some characters that no longer matters. Some of this is thrown completely out the window.

Halsin and Shadowheart are suddenly lusting for each other, though in the act before they were bickering like a father and child. The disconnect here was jarring!

Halsin and Astarion is just as baffling. They have absolutely no common values - and druids dislike vampires.

Halsin is supposed to be the symbol of ultimate personal choice, agency and freedom, but actually is rigid ultimatum of "We do not discuss this. I am telling you this and you accept, though I have been emotionally encouraging you for two whole acts."

Shadowheart goes from "I don't want just part of you" to "I want to share you with world".

Astarion goes from breaking up with you if you "use him physically" to being (and I am sorry) coerced into suddenly accepting you being with Halsin also.

Now, my question is:

What happened to Shadowheart and Astarion, and the hints of that slowly being a thing in EA? Why was that not implemented as a healthy polycule instead? Shadowheart says "He needs you more". Can I ask why Halsin doesn't have this mental awareness for as wise as he is supposed to be?

Shadowheart and Astarion often have shared values, and being with you from beginning that could have blossomed into something healthy and secure.
Instead: "So you want to be with Halsin because I'm trying to get comfortable with physical touch again?" WTF?

Another option for it: Karlach and Halsin as being Tav's polycule. They have shared values, they have some funny banter in act 2 and are in a different place than the others.

Add two camp followers as extra options, and you have more diversity. (A non-binary would be nice).

I don't understand these choices at all. Representation was just there, and it was lovely. So what the hell happened?

What is even more baffling about all of this is that you had this entire Twitter X campaign about "Players being punished for objectifying Astarion". Yes, alright... Where was this piece of "awareness" during the process of writing this and especially Halsin?