Halsin is clearly not written in a way that considers Tav rejecting him. Which is weird.
I mean, there's a lot of things wrong with his romance overall, but if we disregard all of that, his romance is best (or rather the least bad) when he is the only romanced companion. It's also a little less bad when Tav's actively romancing someone else and wants Halsin on the side. But when Tav wants exclusivity with another companions, Halsin's clearly a real creep. Did they really not consider that there are players who DON'T want to romance Halsin in any way?
Personally, I really like Halsin and I have such a hard time accepting that he's actually meant to be this creepy sex-pest that only thinks about himself. It doesn't feel like that's who he is from everything we learned about him in ACT 1-2, everything about it just feels like a massive mistake (and I'm not talking about him being poly and fluid).