My way to have him never annoy me. Do Thaniel's quest WITHOUT having him in the party, done, saved the boy good Act 2 ending. And yes, without Halsin, no saving the kid. Then Ignore his existence, never even talk to him, imagine him just as what he really is, a forced NPC you must have in camp to have a certain quest done. I did it, and boom, all my problems were solved. Still annoys me having to avoid any npc, but honestly, I didn't miss a thing not interacting with the unpleasant horny weirdo dude.
That's the way I'm playing it (the Lift the Curse quest is done apart from killing Thorm). I can't stand Halsin from the moment he opens his mouth in the goblin cells. I'm hoping for a mod which allows you to kill him (and Volo, another waste of space I can't get out of my game).
