
I have to say as much as sasya's behavior is driven by trauma and just a basic lack of understanding of how human relationships should work, his complete obliviousness to his role in karel's pain is starting to get annoying. he's so deluded in his thinking it's hard to believe someone like him could have a professional dancing career.

Does he not know that she knows he had her nanny murdered or is he taunting her? I can't tell if rezef respects her or thinks she's an idiot?

He doesn’t see her as an idiot but he believes she can only know what he shares with her and she should only act on his tune. It was also a sort of warning because she wrote and invited nanny to the palace without informing or asking him. Nanny has no reason to kill herself especially after replying to the fl and saying she will come to the palace. By killing the nanny he is telling her she can’t have her own people in the palace so in a roundabout way he is admitting that he killed the nanny but he doesn’t know she actually witnessed the murder. Basically he is an obsessive creep whose obsession has far crossed the border of incest.
the duke is a walking red flag.