Honestly, I don't think that this is the kind of thing I can ignore now that I know about it. I'll try to explain how I came across all of this. I played the game with Shadowheart as the only companion I actively tried romancing. I thought it was great, the slow build up was nice and I thought it felt rewarding. I was randomly scrolling through the feedback threads on Discord and found out that people weren't satisfied with Halsin. Then I found this on Reddit:

https://www.reddit.com/r/BaldursGate3/comments/173s56w/act_3_halsins_behaviourheavy_spoilers/

Not long after that I found the orgy scene on Youtube. Basically implied that you and the drow twins watched Shadowheart and Halsin go at it. Again, I can't forget that kind of thing. Her romance dialogue points towards her being interested in you and only you and not being okay with an open/poly relationship. The fact she's suddenly turning 180 degrees for Halsin or becomes interested in a foursome is jarring and the fact that this thread exists at all with it probably being at least top 5 in terms of popularity here speaks for itself.