
Victims of abuse, especially since a young age like Yigon, are conditioned by their abusers. It's not something that suddenly happen to you, it's progressive. By the end, when everything is as terrible as it's right now in the story, the responses are automatic, no thinking is involved only learned reaction/inaction.
Go watch the tv show "maid", it portray that really well and also shows how abusers exploit the victim's vulnerabilities.

Yigeon not just mad at Taekang, lol.
He simply can't trust Taekang anymore. Did you even read or just forget the plot?? How the hell Yigeon trust someone who suddenly acted nice after all the horrible accusations he put in Yigeon??
Yigeon DID try to seek help from Taekang, instead Taekang called him delusional and all the accidents are just Yigeon's bad luck.
I have to say that Yigon is a complete idiot. I understand that he is mad at Taeyang (male lead, I don't know if that's his name right now). But I wouldn't do anything that my so-called brother, who wants to kill me, tells me. If he gave up, then if I were him, I would tell the brother "Get it over with and kill me, you psycho" and honestly, I wouldn't believe a word the brother says. Such an asshole.