
I don't know how this will progress afterwards, but this chapter is pretty much expected and very light (on the bdsm part). Since the main content of this story is just Alex and DG's relationship, I guess many readers are not used to reading about bdsm relationships. That slap's the lightest thing you should get used to if you're someone's sub. MD's been really easy on Chanwoo until now (from what we saw, which is not much), so Chanwoo's quite spoiled as a sub and I hope that kicks some reality in for him. This relationship was never professional from the beginning because Chanwoo was in it for the fun without knowing what bdsm could become, and MD was too considerate and spoiling him since he has feelings toward Chanwoo.
I would flip too if Alex were to slap DG, but since it's a dom-sub relationship between MD and Chanwoo (and they both agreed to it, with a safe word), I think it's totally normal and it could be worse (doubt it tho because MD treasures his boy so much). If people can't handle this slap I think it's best that they stop here so that their impression of the story will still remain the way they like.

Everyone can see it was revenge. That's why I said the relationship was never professional. What did Chanwoo expect? Continuing this purely sexual relationship when 1. You know the other party likes you romantically and 2. You want to have a boyfriend? I don't think MD's in the right, but Chanwoo should have been able to see that coming.
If Seunghyun were not into MD but Chanwoo, I would honestly feel bad for Seunghyun It's one thing if your boyfriend has a bdsm relationship with another guy, no attachment, but he knows the other guy has feelings for him and still wants to continue it.
I don't think Chanwoo's been wronged. He has the right to fuck or date anyone he likes and vice versa, but he should know he shouldn't want too much. If I were him, I'd just end the relationship with MD (and then he can live his life the way he wants, probably find another dom that doesn't like him and is alright with him dating others if he's still interested). But I'm not Chanwoo or the author so it'll go the way the author wants, aww.

Yeah I really appreciate that he asked many times, and that shows even more clearly that Chanwoo's NOT involuntarily in it.
But I do think it was some 'dirty tricks' MD's got there, not normal discipline. I don't oppose that tho because actually even though we're in the last few chapters of this manhwa, their romantic relationship's still in the very beginning phase, so it'd be annoyingly unreal if the normal caring MD could change Chanwoo and take him home just like that. Hence this may help escalate it a little. But we don't know yet until the next chapters, so let's stay tuned and see :)
I think Miyai's going to be the end of the sensei's reign