it was because of his father (the bottom's father) if I'm not mistaken.. his father threatened him if he's not doing what his father wants, his father will crush Aaron career or something, so yeah, he chose to go into hiding than do what his father wants. Kinda forgot.. but the reason is because his father doesn't want him to be happy since he "killed" his mother ┑( ̄Д  ̄)┍
I think it's the abuse that's making him run. Victim's brains are always wired differently. If yujin was mentally healthy he can give no damn about what other ppl says and let Aaron handle everything. Realistically speaking, Aaron can crush Yujin's father anytime. He is only refusing to do so bcs of Yujin

Why the bottom always run off...it's not like he threatening you he can take care of you way too well come back yujin