The black hair boy likes to watch his friend get groped in the train since he is a sadist, and the teacher is also an sadist who is involved with the black hair boy in the last panel. So he is thankful that the boy in the last panel isnt like the other boy from the train even tho they look alike.
Idk if you want me to exlain it for real but:
The black hair boy likes to watch his friend get groped in the train since he is a sadist, and the teacher is also an sadist who is involved with the black hair boy in the last panel. So he is thankful that the boy in the last panel isnt like the other boy from the train even tho they look alike.