Development time is limited. There is a finite amount of development time. Resources are limited. Budget for recording new voice lines is limited. Time and budget that go to develop negotiations for a mono/poly romance track, or to develop a challenge/disagreement romance or friendship track, are time and budget that aren't going to the already-present tracks of "no romance agreement/friendship" and "yes romance agreement/romance." Those two RP tracks, already present in the game, are what I hope receive the limited time, resources, and attention the studio affords to Halsin.

He is not an origin. He is merely a recruitable companion, with many 50/50 choices on the player's part to not have him join the party at all, so his development time and budget will already be quite small since he is not an origin. And that makes sense! I would not want him to receive a larger portion in terms of ongoing development than Wyll, for example.

Halsin's development time might have already concluded, but if there is any chance for additions, the direction those additions go in, in my opinion, should not introduce more tracks, but should develop more content for his two already-present tracks in the game, neither of which involves any emotional blackmail, neither of which involves manipulation or abuse. And to address those feelings in players, budget and time going into somehow flagging with complete clarity for players in Act 1 that he's into free love and romancing others won't lock him out by the time he's available in Act 3 makes sense.