Himura-sensei no Junan(2010)

Himura-sensei no Junan

Himura Yuu is a high school doctor with a serious shota complex and there's only one person standing in the way of his virtual smorgasbord; his colleague, Ashiya. Himura is clueless as to why Ashiya interrupts him everyday, but when he learns of their previous connection, things become all too clear.

(Source: Blissful Sin)