Originally Posted by Mordred92
As far as I know that kiss was created specifically for Astarion and Karlach as a first kiss.

I could be wrong, but I don't think Karlach even has this kiss with Spawn Astarion in Act 2 anymore? It's likely it was given to her by mistake initially.

Originally Posted by Marielle
Astarion doesn't want to control Tav.

He says in dialogue that relationships are a form of control, and a devnote for the attempted turning scene with Karlach even directly says he's thinking about controlling her.