Kimi ga Konna ni Amai Nante, Shiranakatta.

Yoori, who works at the hospital as an inspector trainer, had a girlfriend Haruki, who lived with him for four years. One day, he's a drunken friend. When he returns to his apartment with Haruki, he finds an unrecognizable pump on the front door! It was the scene of Haruki's affair with a woman she doesn't know that jumped into the eyes of Yoori who didn't have a bad feeling...!