The Brightest Place on This Planet(2016)

Kono Hoshi de Ichiban Akarui Tokoro

Yuki Hayakawa has cherished Takao Mochizuki since they were kids, but now Takao has found someone more special... Yuki comes out of this love triangle feeling defeated. Takao's homeroom teacher, Mr. Kanda, offers to comfort Yuki and suddenly kisses him, whispering, "I've been watching you all this time." Feeling sad and lost, Yuki lets Mr. Kanda make love to him... Where will this relationship that started with a physical connection go? This is Nako's debut manga about a mature teacher and a broken-hearted, hot-and-cold high school boy! Includes a bonus page and an extra bonus page exclusive to Renta!.

(Source: Renta!)