
I just can't understand why heiner would want to tarnish her, bring her down enough so that he doesn't love her and no one loves her, when he in fact does love her and he's just doing all those bad shit to the one he loves @.@

I mean tbh it makes sense to me (not like in a way that I would also do the thing but in a logic-ish way).
She was this immaculate figure in his mind keeping him going when he was going through actual literal torture. When he saw she was just an ignorant noble woman, he simultaneously became disgusted with her and with himself. He didn't like how much importance she still had to him. So he wanted her to become as far removed from that immaculate figure he had in mind of her, to become "ruined" so he wouldn't have to feel that conflicting feeling of disgust. He loves her in that he can't live without her, but he doesn't want to love her (and that's a big factor in relationships). He doesn't want to see how she's changing and being affected already by things and doesn't want to see her as more than an abstracted, simple noble woman because then he would have to confront his feelings and what "ruining" her actually means.
Ahhh so fluffy and warm uwu