For the same reason why all narcissists and abusers are obsessed with their victims: easy mark to control means easy way to continue to pretend to be a normal well-adjusted human. They lack confidence in themselves and view themselves in a poor light, by having someone need them, they feel better about themselves and by abusing them, they “get rid” of the negative feelings. They put a lot of effort into perfecting the art of abusing someone just enough to keep them satisfied and love bombing them just enough to keep the victim around. It’s a hard process for them to learn since each individual is different. They end up in a codependent state to their victims and think of themselves as better since they would “pick up the trash” a second time. It’s classic abuser psychology.
Why is the older brother so obsessed?