Responses
He doesn't 'like' her, he's obsessed with her as you said. He sees her as an object he can use with no consequences. A tool, and a 'tool' to him shouldn't give its loyalty anywhere else. He wants to control her completely. Ruby is being 'nice' to him as you put it because she's afraid of him, she's been a victim of abuse for years and this is her instinct in order to protect herself and the people she loves.
Does anyone know why Caesar is weird? he likes ruby but he still hit her. He is obsessed with her but would married off her to others? And why ruby is nice to him even if he hits her?