I agree, Halsin thing needs to be resolved. I don't think they will make her full mono though, requires too much rewriting. I don't think this is a bad thing that she is "open monogamous". She is very clear what she wants and needs and in the end you still will get your happy farm ending with kids etc. Remember that she is happy with your Tav and never asks or does anything on her own(poly related).
Well I completely disagree and I am not okay with your "open monogamy" take. Without a way to get her to explicitly state that she would only ever want your character if that is what you desire then the door is always open to cheating or her trying to open the relationship herself with the current way she is written.
But she never suggest herself and happy with Tav, no ? It's Tav who tehcnically can do it. Bold of you to think that she would cheat(I get where this all coming from, her problematic SH/Halsin banter). She never asks "hey lemme fuck Halsin/Karlach"(or something like that). Thats why I think that would be cool to have a dialogue to state your boundaries and what you want from relationship(tell her that you are exclusive couple as example, I don't think she would have anything against it).