He was trying to help him but that was what he got in return. And he was a man with a family, too... And nothing was done to make it up to him or for the main character to deserve the sensei's forgiveness. I get that he was a very very messed up kid but... That was another person and his family's life possibly ruined (because losing your job as a teacher due to sexual harassment/scandal or any other immoralities is very very shameful, not only for the man/father but for the family as well. And the fact that it was false makes the situation even more bitter to let go. It's hard to clear up your reputation)
Tsk. Ah well, he did go through a lot of shit anyway, that 'uke' (i hate saying uke but I forgot his name, so...) But with all the bad things he did, I couldn't help but think it was his karma balancing things. He didn't deserve the bad stuff for no reason, but because he did the person who tried to help him wrong, he received a lot of misfortune. The only saving grace he got from his punishment was his child. His karma was getting better after that lol

*whisper* ₕₑ ᵣᵤᵢₙₑd ₛₒₘₑₒₙₑ ₑₗₛₑ'ₛ cₐᵣₑₑᵣ