
That slap was not necessary that was not part of the BDSM chanwoo was not comfortable with the situation but he wants to keep his relationship with MD. I'm so upset right now

Yeah roleplaying in this play where he is letting his personal feelings navigate his actions...not a safe environment and shouldn’t have had to happen at all. They could have just talked this over but MD decided to use his dom role to force chanwoo to make a decision instead which is a dick move and just part of a power play

Imho. I do not think MD is doing a revenge play, I think that is out of character for this guy. I do not see a problem with an open handed frontal slap (it is not a punch, not a backhand slap--those can actually do damage) from a D to his s unless their contract expressly prohibited it but the writers didn't show us their agreement so WE ARE ALL SPECULATING, you choose to speculate that isn't allowed and I'm playing devil's advocate. A sub's role...his desire...is to please his Dom and his Dom wants Chanwoo to make out with the other sub. I think MD smirked because he was please that this is perfect training opportunity for Chanwoo just fell in his lap.
MD wants Chanwoo to stop chasing after physically and emotionally abusive boyfriends and to use the safe word when he's pushed beyond his limits....
Chanwoo was attracted to this other guy and prob wouldn't have had an issue making out with him at MDs command but since he was told he was only being used, making out with him while trying to be sexy to please MD is gonna be hard and uber humiliating even for Chanwoo's masochistic level..
Chanwoo is not afraid or unsure here...he is feeling awkward in front of MD, worried about the prospect of losing his position as a sub because of the other guy, and he just took an emotional kick to the gut upon learning he was used by this kid who wanted MD back. (If you think about it, MD barely remembered this jerk and clearly tried to cut him off completely way back when, if Chanwoo wasn't so flustered he'd realize he has the advantage. Also for all we know this is a job interview/audition, passing or failing doesn't necessarily mean they can't continue to be play buddies off camera.
So, I think maybe he is being trained in a roundabout way.
Ultimately I think MD is trying to help Chanwoo come to terms with this dependency, I really want to see how this plays out.

True we are all speculating at this point. The smirk was still the thing that made me dislike this though because MD chose to take the passive aggressive/petty road to get chanwoo to make up his mind instead of just talking it out. I admittedly have never been in a sub/dom relationship but I would assume that they’d need to be open about everything and be able to talk things over which clearly is not happening here. I think they are both making poor decisions at this point. I just hope this isn’t dragged on for like 20 chapters because that would be hard to read
I- there was so much tension in this chapter I had to hold my breath reading it
It felt like I was in the cafe and couldn’t take the heavy atmosphere