He does have a tragic back story, but his thinking and doing is wrong

Its also in his pov so we don't see him abusing her

in his mind he does not abuse her. He also skipped in the flashback the moment he did it for the first time. So he is now in a point so deep in his delusions that he only see what he wants.

The good thing about it is that it is about to be over (The flashback)