Mimoza no Kokuhaku

Growing up in a dreary suburb, Sakuma has little to brighten his humdrum days aside from his best friend. The bright, talented, and attractive Ushio seems to have everything Sakuma lacks, and his academics and athletic prowess make him popular with the girls at school. Past trauma—and an understandable inferiority complex—slowly drive the two apart, and by the time they enter high school, they hardly even speak anymore. Thus, Sakuma finds himself alone.
Against all odds, he eventually gains a friend in Natsuki, the sweetest girl in class. The two hit it off gushing about their favorite novels, and he falls head over heels for her. But that very same night, he stumbles upon an unexpected sight while walking through a familiar park: his old friend Ushio, dressed in a full-blown schoolgirl’s uniform and sobbing uncontrollably.
(Source: Seven Seas Entertainment)
Note: Includes 5 extra chapters.