I think it was a bad ending if u carefully read the end, I think he cut it off with hansol and kwon, also that empty seat is probably kwon's seat so maybe he ended up migrating with his uncle, his grades dropped even more u can see it in the papers, his dad did the Same thing again and we can see him falling to what I presume to be his death, he likely committed suicide
Personally I feel like you're just left with an empty option, either one, your thinking or two, everything got eventually better and it was has anxiety at the end. Or three, nothing changed in the end as if he didn't meet the friends he made.
Wow... What the fuck just happened.
The fact you're left with the option if he had a good ending or a bad ending is just... Wow.