Because he is his dom.... And he wanted his approval and see if MD wants to continue their relationship after he got a bf. And can people stop saying that someone deserves abuse. It's seriously sickening.
It's bdsm not abuse.
BDSM where dom is mixing his feelings and grudge with a play? Where he is taking his anger out on the sub because he had audacity to reject him? Where he makes sub participate in the play and things he is uncomfortable with under disguise of BDSM scene? And he knows sub won't refuse because of conditions he put on him and they are impacting his choices. What's more it was shown that Chanwoo has problems with limits, he didn't say anything while being strangled to death and MD is fully taking advantage of that. He isn't interested in the other sub in the slightest, he is just getting petty revange on Chanwoo.
This isn't good or safe representation of BDSM.
I mean. You even wanted to introduce the guy you want to date to the guy who likes you and you rejected. You pretty much understand that that would hurt. Now you ended up being the one hurt, you deserve it..