I mean, it sounds like Halsin had every reason to assume the player had their partner's consent if the player and Astarion were already planning on having an orgy. It wasn't the factually correct assumption, but it was hardly a wild leap of logic to take. What's the alternative? Halsin sees a friend ready to have sex and goes "wooooah there buddy, are you sure you're not cheating on your partner?" Dude, that would be the biggest asshole move EVER.
It's odd that he would assume it there when he is very adamant that there is explicit consent from your partner in the earlier scene. I would chalk it up to the scripting and depth of that scene not being very thorough. The complete lack of reactivity from your romanced partner that you went behind their back suggests that they didn't bother thinking too hard about consistency and consequences in this scene.
If my friend was in a monogamous relationship with someone and about to do something that would really upset and hurt their partner, I would 100% call them out on it and I would certainly not want to be complicit in it. I really don't see where that makes me the asshole.
Honestly, that just sounds like a euphemism for "I'm looking for excuses to hate the guy." The writers didn't open Pandora's Box- the portion of the fanbase that feels possessive over pixels did.
This is what I would rather assume. With it requiring utilising specific flaws in the scripting to set up the situation, I think you would need malicious intent to go through all that just to point a finger at Halsin saying how awful he is. As I said, I find Halsin generally likeable, there's just a few places where they have made some mistakes with the scripting and writing, and if you go out of your way to find them, it makes him look very out of character. Rather than seeing these things as canon and finding some warped logic to defend them, I would just assume they are attempts at jokes or glitches and avoid them.
