Shoya Kare: Ijiwarude Amai Hito

Miku, an office worker who's terrible at romance, is rescued from a difficult situation at a company drinking party by her ex-boyfriend, Kosei Sugiura...!? What's more, they end up becoming closely involved with each other both at work and outside of it!? He's mean, but sometimes sweet, and it's all very confusing! A second chance at love with an ex-boyfriend boss!

(Source: Kodansha, translated)