Let's see...
MD crossed the boundaries of the play three times. He mixed his own, personal feelings, anger with the play which is just unacceptable. He nearly strangled Chanwoo to death because of anger after rejection. Then he coerced him into the play with other sub. Just after he was betrayed and rejected he put ultimatum that he will abandon him too if he won't participate. Clear emotional manipulation, it's no consent if it's impacted by condition. Chanwoo was pressured to take part in the play with the guy who just used him. He was anxious, disgusted and only stayed in the play because of ultimatum. He is abuse victim and MD knows that but he out him through another super toxic and traumatic experience because he wanted to see his reaction.
It wasn't BDSM it was abuse disguised as one.
I don't get why people are trashing MD. Chanwoo always had the right to stop the play by saying the safeword like he did in the threesome. MD also made sure to let him know that he could stop at any point. This is so much better than reading glorified bdsm.