I reckoned it was Seungho. He attempted to get answers from NK (for NK to share what's on his mind), but NK doesn't tell the truth so Seungho realized that they're just eff buddies.
I think NK wants to forget about the teacher and not have to think about his situation so hes made it easier on himself mentally. Like a person who chooses to have no expectations from himself in fear of rejection or failure
Uhh so wait who was speaking at the end?