They both have some type of brother complex although not severe that's why lol
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That's why tae-ui too doesn't like raman no matter how creepy he seems
It's not a spoiler but you're supposed to understand from what Taeui said previously, that Ilay has been obsessively chasing him around. Jaeui doesn't like the fact that Taeui has gotten entangled with a madman for the long term
I've read the novel and all the side stories and jae-ui never disliked illay before even though said mad man tried to shoot him but when he saw the emotions hen invoked in tae-ui he just got a little jealous. Even tae-ui later says he doesn't like raman cause "he feels he's going to steel something precious"
Why did he became speechless and say he's going to hate ilay from now on?
Its like he realize something..