No Strings Attached (2013)

Blurb:
Yuko and Kazuaki are regulars at the same bar who never particularly connected with each other—until they end up in bed together one night. On the way home, though, Yuko experiences a shock of sorts when Kazuaki says to her "Just don’t fall in love with me, okay?" Regardless, Yuko plays it cool—but is a relationship with this kind of detachment really what she’s after . . . ?

Source: www.anisearch.com/manga/17398