Inu to Kuzu

Sakuraba Haruma's childhood friend Inukai Shuji was a cut above him in every way imaginable, living out the glamorous life bestowed upon him. Haruma, an unassuming salaryman, has lived his every day clutching onto his inferiority complex, existing only in Shuji's shadow. One day, Haruma coincidentally meets Shuji's wife, Inukai Reika, who Haruma has always secretly admired since his high school days. With feelings of envy, jealousy, and more, a "secret" is born from Haruma's repetitive days.
(Source: MyAnimeList)
~~ Adapted from the manga series "Inu to Kuzu" (犬と屑) by Asaga Iori (朝賀庵).