I kind of forgot but why did he run away again?

Think it was to prevent his dad from interfering and hurting Aaron

His father revealed to the whole world that yujin is the son of the man who kidnapped aaron. Yujin had a major freak out that being with him was gonna ruin Aarons life and carreer because his father will keep interfering. Yujin seems to have major ptsd because of his dad. That made him run away so that he wouldnt get him further involved.

Oh man. Thank you guys.