My Ultramarine Sky (manga)

From their first year of middle school to their second year of high school, Kai and Ren have not only always been in the same class—they’ve also always sat next to each other. But in their last year of high school, the boys are assigned to two separate classes, and with each passing day, Kai feels as if he’s slipping further and further away from Ren… One day, when Kai finds Ren sleeping in a classroom after school, he whispers the feelings that he can’t bring himself to say out loud… and Ren hears him. Will Kai’s confession draw them further and further apart, or will it be the spark that brings them back to each other once more?