BOTH of them are pmo bro, it's not just Aaron's actions but also Yujin's constant LYING I will not excuse the way Aaron decided to handle this situation (how the AUTHOR decided to make Aaron handle the situation) but I will also say Yujin's approach was also not mature. He led Aaron on and then left just like that, ghosting the other, leaving a bigggg gap in their relationship. I know that talking about his situation with his dad is hard and stuff and this is fiction, but usually you communicate at least a LITTLE, he wants to save Aaron but then doesn't tell him what he should be careful of. It's just keeping him in the dark. And at the end, Aaron also tells him that his lies are getting too much, Yujin just decided to provoke him even more, though maybe the situation called for it. Still wasn't right and it escalated it.
I hate when authors put hardcore kinky stuff but it's never in a bdsm sense with actually clear consent... sighhh this would've had better potential