The way I understand it is Yujin felt that him being around Aaron made him a target for his dad, to hurt Yujin I’m assuming. The crash Aaron had was because of Yujin dad, and then the article coming out about Aaron’s boyfriend being the son of a criminal just tipped him over the edge and he disappeared himself to protect Aaron.
From what I understand, Yujin blames himself for his father targeting Aaron (like in the car accident), so he ran away to prevent Aaron from getting hurt even more. I think there are still things that need to be explained, for example, the connection between this guilt Yujin feels and the attack on Aaron when he was a child.
Why did yujin leave? Im sorta confused. Did he leave bc he was the son of the man who tried to kill hunter?