You'll find a number of long-time Halsin simps on this forum, myself included. I haven't seen any of the others offer their opinion on his romance yet; here's mine.

Like you, I was disappointed to find myself in that either/or situation - either accept non-committed non-monogamy (from him) or abandon ship. But I also have to say: I was basically expecting this. It's very much part of Forgotten Realms lore around elves, especially wood elves (and also very much a feature of bears - which he's closely identified with). From a more meta perspective, since he was a late addition and his romance takes so long to kick off, I can see why they worked things this way; it causes the fewest conflicts.

Fortunately for me, I have plenty of headcanon to use in working around issues like this, and I mostly enjoyed the romance. As a dyed-in-the-wool monogamist, I'd be interested in hearing opinions from folks with a different perspective on relationships. Based on what I've seen elsewhere, some enjoyed it, some had issues.