Right?
Chanwoo called the safeword, MD completely obliged to it the moment it was called. The reason the safeword exists is to make sure lines aren't crossed because there is a big chance that they can be depending on how far both parties are willing to go and how extreme they may want their play to be. In some chapters, both violated those rules and we see it weigh both of them down emotionally, but here, we see the rules executed as they should be. A dom relies on their sub as much as the sub relies on their dom. That's how it is.
Chanwoo was given a choice from the beginning. MD was asked by his previous sub to be his dom again, and then rather than objecting, Chanwoo went along with the situation, got into the outfit, and followed orders as he would with their usual play, then continued time let it go as far as it did knowing full well he could have given a safeword as soon as he was too uncomfortable.
The same way Chanwoo had no obligation to date MD because he didn't have feelings for him, MD had no obligation whatsoever to keep Chanwoo as a sub. He had every right to say that he would keep the old sub, especially if he no longer wanted to continue play with someone he had feelings for. MD may have known what that may have made Chanwoo feel, but that doesn't mean he didn't have every right to say it, nor does it mean that MD was forcing Chanwoo into the play.

PEOPLE COMPLAINING ABOUT BDSM HERE SHOULD GO BACK TO READING VANILLA. SO MANY FUCKING WANNABE PREACHERS.