I can see them getting mad if they thought he was faking it but I don't get how they can get this mad at an amnesiac. Why is his body not being able to handle alcohol being treated as if he purposely wiped his own mind like he's a droid from star wars. I don't know if this is a cultural double standards sort of thing or the authors own perspective of where the blame lies, but I have a strong suspicion that if the shoe were on the other foot and Gwangchae was the one who forgot that they were dating no one would get mad at her at all.
This is almost as dumb as if for example everyone was constantly mad at the chick from "50 first Dates" because she kept forgetting she was in a relationship because she had anterograde amnesia. How do you blame someone for something that is beyond their control?