I think the idea is that he doesn't actually hate him, he just acts like he does because he doesn't want to be left out. He has abandonment issues.
I think his initial hatred toward the other kid felt exaggerated, and now when he's suffered through all that he shows that he kinda likes him anyway? I mean, what happens in a story happens, I just feel that it doesn't make much sense here. It's all too romanticised.
╥﹏╥
Spoiler.........
He dies
Spoiler................
he doesn't
You save the day
imagine the kid you hate getting adopted by the person you admire and look up to most in the world while you get adopted by a piece of shit who cares more about money and his work than his own child's health and happiness
i'm surprised bai ming grew up to become a much better person than he was when he went through all that! ugh he's totally my favorite character, i hope he recovers well