Ochiru Seija no Seppun manga is a popular manga covering School life, Smut, Yaoi genres. Written by the Higashino You. 8 chapters have been translated and translations of other chapters are in progress.
From Fantasyshrine:Okano-sensei, a high school teacher, was sexually molested by a pervert in the train on the way to school. As fate would have it, his student, Tokiwa, witnessed the whole incident. He then threatened to expose Okano for having a fetish of being groped by a man unless Okano agreed to be Tokiwa's sex slave! In shame, Okano succumbed to the pleasure only Tokiwa could provide