Green's manga / #Classmates(229)

Vol 2 - Ch 9 - p30

Ch 5 - Popular, perfect good-looking high schooler gets compared to an even prettier boy, Kougami. Outraged, he vents his frustrations in a secluded bathroom, and accidentally gets heard by a student eating lunch alone in the stalls. After many heartfelt sessions of mutual understanding, Senpai suddenly finds himself attracted to this mysterious kouhai, Tanaka-kun

I saw people asking about which manga is in the credits: Ushiro no Seki no Katou-kun Yeah, screw this manga and read this fluffy manga instead :)