Boku no Suki na Sensei

Overview

Kenmoto Kazuki is a 15 year old high school student who is late for school on his very first day. As he's running to school he sees someone ontop of a wall that warns him not to go through the main entrance. Without a second thought he blurted out three words, "Please marry me!" From the shock the person falls off the wall where Kenmoto Kazuki discovers he just proposed to a man. This man was not just any man, but Morikeoke Akitou his homeroom teacher! Included one-shot: Volume 1: Karada no Yuuutsu

Source: AniList