I think I kinda get what teacher is feeling.
I mean the person he loved the most and had been his strength during his harshest times ended up falling for another person instead of him. Plus add that to his dying out passion for his work, declining mental and physical health, and a rare support system being there for him (I know Yuri's there but he's a shitty type of support tbh).
I seriously think he needs therapy but this is a manhwa so maybe it'll magically disappear at some point. sigh
And this is why kids! make sure when you want to reject someone you won't end up looking for them!
Also make the challenge hard Kangjoon! I want that jerk to suffer first