@Rover , He's THAT bad. Someone like him knows what he's doing, in fact there is NO WAY you can't notice that you're breaking someone down, causing them pain and torturing them. He knew. And continued it. People like him can rot in hell.
He slightly makes me think of the older brother in mahou shojou site. He might possibly either feel pressure from having to live up to people's expectations consistently and takes it out on his sister/ he is someone who only finds joy in tormenting her.
OR
her memories could be wrong because she did say something was missing.
But as of now, he's a big b/st/rd who deserves to burn in tartarus.