In Act 1 everyone is in a flirting stage, some companions come at the PC harder than others but it's all fair game so to speak. In Act 2 the relationships tighten and the PC starts being exclusive with one romantic partner and the topic is settled. It seems obvious to everyone else, that the chosen relationship is exclusive. The way in which Halsin, who witnessed all of this, approaches the PC in Act 3 is focused on what he himself desires. He considers the preferences of the PC, their partner or their commitment to each other only as an afterthought. So there is a big difference between Lae'zel and him.

I'd assume that - brothel aside - if he just opened with asking the PC wether they are more of the wolf or the bear inclination, his proposition would cause a lot less bad feelings.

Yes, that poor little tree!