Koi Shika Dekinaiyo

From Fantasyshrine: Love Alone Won't Do: High school teacher, Umehara Akio, drew a problem child, Hataoka Kei, out of his home and back to school. Years later, Umehara got transferred to a new high school and met Kei again, who’s working as a delivery boy for a florist shop. Seeing his former student grew into a super good-looking college student, Umehara couldn’t help feeling proud. What he didn’t realize was Kei’s true colors… a pervert who molests his drunken, unsuspecting Umehara-sensei!!