Completing Bronka's quest allowed her to confess her feelings to him, which led to their marriage.
Kosha probably doesn't fully realize the significance of this fact, but in expansions, players rarely manage to do something good. Usually, they are either a tool in the hands of evil or simply unintentionally ruin the lives of NPCs (see Nora). Congratulations! 🤗
Added after 31 seconds
Oh, and Arandor commits evil acts fully consciously and intentionally.
Where do we end up when we save the world?