It all started from Jeha kidnapping him though. It doesn't matter if they like each other or not. It's shitty of him to treat Myongrong like that. Basic human decency, even for a stranger. At the beginning of it all Myongrong had nothing to do with what his sister did or doing but Jeha still treated him badly. While Myongrong had been acting carefree all this time because he's positive doesn't mean it was good? He's been beaten, shot, locked up,etc...
YEEEESS! 100% agree! Jeha has been treating Myongryong like shit honestly, kidnapping him, imprisoning him, treating him like a prostitute and sending him away to some pervert etc. And as you said just because Mongryong usually acts carefree doesn't mean you can treat him however you want. Jeha deserves to feel bad about it and imo he needs to work to be forgiven. Just because he will treat him better from now on doesn't mean the past is undone.
I don't understand why everyone's hating on Jeha for what's supposedly going to happen, when from his point of view Myongrong doesn't like him that way and keeps bringing up the brother all the time. Neither of them are better than the other. They're both stupid as shit and deserve one another