
well, if you look at it in a different perspective, true. chanwoo didn't like MD back then but he still broke his heart. chanwoo also didn't take MD's advice about 'dont date anyone because of their looks' thing and look at where it got him. (spoilers ahead)
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the new guy was just using chanwoo so he could end up with MD. he didn't really like/love chanwoo, he just used him so he could meet with MD, and start a competition that didn't really had be thrown.

So you’re saying chanwoo should’ve just ignored his own feelings and date MD just so he wouldn’t break his heart? Are you reading what you’re typing. It was not chanwoos fault that he didn’t return his feelings. Yes he was wrong for dating yet another guy because of his looks but if you go back and read it again he was also interested because they were into the same things and not just because of his looks but it doesn’t really matter since it turned out this way.

Chanwoo should be able to do whatever the hell he wants.
MD doesn't own him or his body.
They said that they weren't dating and they even had partners outside of their "relationship".
Chanwoo shouldn't have to be slapped or embarrassed just because he doesn't feel the same as MD.
MD was wrong in doing that.
There is a different between a bdsm slap vs the one MD made.
MD: Date me, I am not gonna hurt you like your abusive boyfriends
Also MD: Imma slap your bitch ass for rejecting me disguised as play
Of course, Chanwoo “KuhNseNtEdddd” to their play, Let’s ignore his reaction when he was slapped. that was definitelyyyyyy consented.