Matte, Ima Kyun to Shita.

Overview

"We've known each other ever since we were in diapers. I thought I knew everything there was to know about him." Natsuo attends the same college as his childhood friend Misaki. Campus life for the two has been going swimmingly. And because of their overwhelmingly good looks, these two never have a shortage of girls lined up after them. At a drinking party one night, Natsuo learns that Misaki acts surprisingly cute and spoiled with his girlfriend, a stark contrast to his usual aloofness. Shock soon transforms into obsession, as Natsuo begins thinking about Misaki every waking moment...! When it comes to Misaki, he has to see it all! His cute side, his body... (Source: MangaPlaza) Note: Includes one extra chapter.

Source: AniList