I Love You, Until Morning.

Hibiki, 28 years old, was dumped by her boyfriend she'd been going out with for five years, but Yusa, her junior at the office makes a fierce move on her saying that he had his sights on her for a long time. He's usually cute, but he's sexually aggressive between the sheets. A secret office romance with a wicked handsome junior begins.

(Source: Kodansha, translated)