Fudanshi-kun ni wa Himitsu ga Aru

Overview

Shion and Sota are in the same class. Shion is a cheerful guy, and Sota is a cool loner. They had no contact with each other at first, but they hit it off when Shion missed the last train one night and stayed over at Sota's room. As Shion starts to frequently stay over at Sota's place, he happens to find a notebook that Sota had hidden in his room. When he opens it, he finds... a sexy BL novel written by Sota, describing action between them! Seeing Sota's shyness only made Shion more excited, as Shion starts to play the same game with Sota based on his own novel...! (Source: Homesha, translated)

Source: AniList