Yes, they were written exactly like this. The plot wanted to show that his fucked up personality made his brother who has some kind of mental disorder awake his criminal side. Not saying it was deserved whatsoever, it's just a cause and a consequence. Not every consequence is proportional to the cause.
for no reason? have we been reading the same manhwa??? in the flashbacks u can clearly see since they first became siblings ml has been ruining mc's friendships bc he's jealous and wants mc all to himself. if u used simple critical thinking skills clearly u would understand mc doesn't know why ml would be doing this but we as the readers know but mc takes this all as mc being a b*tch to him and has every right to be a c*nt to him
gonna copy and paste what I said in the precious response:
for no reason? have we been reading the same manhwa??? in the flashbacks u can clearly see since they first became siblings ml has been ruining mc's friendships bc he's jealous and wants mc all to himself. if u used simple critical thinking skills clearly u would understand mc doesn't know why ml would be doing this but we as the readers know but mc takes this all as mc being a b*tch to him and has every right to be a c*nt to him
Everyone is an asshole, only the senpai is a poor victim, I hate the mf MC and his crazy brother, like we say here in Brazil: "i hope they enter each others assholes and explode"