Inu to Kuzu

Haruma Sakuraba's childhood friend Shuuji Inukai 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 Shuuji's shadow. One day, Haruma coincidentally meets Shuuji's wife, Reika Sumi, 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: Kodansha, translated)