I don’t know if he’s being vulnerable or manipulative…

I was having the same thought...but I'm leaning more towards him being manipulative

Maybe it's both. If he lets this little bit of vulnerability show he can manipulate him into doing what he wants.

i think he's letting himself be vulnerable for a change, maybe hes sick of surface level intimacy and is wanting more with jinwoo. but since its his first time doing this, his feelings are unfamiliar and he'll do smth extreme