HOWEVER there was an exception to this. If Astarion was in the party (I was not partnered with him), the Drow twins would invite Astarion. Astarion agreed, and if the player agreed to that, then Halsin asked if he could join. So in that particular circumstance, Halsin does not care if the player cheats on their partner with him. I'm hoping this was just a programming oversight (since in his confession scene he says he wants their consent), but it is something that can happen in game.
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.
Now I know that this probably wasn’t the writers intentions with Halsin, but it’s like Pandora’s box in that once the unfavourable things come out, they’re basically impossible to put back in.
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.
