A guess:
Jaekyung found someone else but he cant forget Dan or he doesn't do as well as when Dan was taking care of him, come crawling back, Dan takes him back, he keeps being an asshole so Dan leaves "for good". Realized his feelings -> come talk to Dan about his "Sad childhood" and they end up tgt.
You know what? I accept it, looking back, he is million times better than Gyujin, he can somewhat respect Sooyoung and protect him. As long he can have Sooyoung's best interest in mind, I think they will be fine
So.. to protect your country....You response was to.. kill the only thing that keeps a big, scary dragon sane..
I think he's stupid man now the dragon will kill everyone
Lol they won't have a country to make the great king roll