I still hope they can come up with more than just the ending. He still lacks commitment (no matter if mono or poly), even the ending is still not satisfying. He still doesn't want to commit, he doesn't even ask the Tav. I mean, lets try to think as someone in Halsin's position: You need a lot of helping hands, you just "saved the world", one of the saviours (who you told is the only one you want) stands directly in front of you. Even if you think this person has better things to do, if your heart is really connected to and in love with this person, you will totally at least try to ask the person to come with you. In the datamined stuff, he doesn't even try.

Sure, imo, Larian never wanted to add Halsin as the main romance for the Tav (something that would be really questionable if you remember all the people who wanted him for a sweet adult romance during EA), so in case you have him as your side kick, it fits the narrative more to just let him go - so the Tav doesn't have to pick between two romance options.