Responses
They didn't have sex
He probably said something but I doubt that they had sex
Jiwon called MD "hyung" which is a honorific for close (older) males used by guys. I think Jiwon just doesn't like opening up to people and he's also a lot more affectionate (probably) when drunk. Hence MD saw this side of him, so its a "mistake"
Spoiler
I don’t know if it’s just me or what but I think Bj Alex and MD had sex before maybe not? Because on chapter 22 page 5, you’ll see they’re at a bar or something and there’s liquor in the background and BJ Alex also mentioned that it was a mistake on pg 6. If you guys read the new chapter 32, you will be able to understand me lol. Since Bj Alex gets drunk easily and it kinda make sense that he would probably do something weird to MD lol