Kanojo, Okarishimasu

Kinoshita Kazuya is a 20-year-old college student who has a wonderful girlfriend: the bright and sunny Nanami Mami. But suddenly, he doesn't. Without warning, Mami breaks up with him, leaving him utterly heartbroken and lonely. Seeking to soothe the pain, he hires a rental girlfriend through an online app. His partner is Mizuhara Chizuru, who through her unparalleled beauty and cute demeanor, manages to gain Kazuya's affection.
But after reading similar experiences other customers had had with Chizuru, Kazuya believes her warm smile and caring personality were all just an act to toy with his heart, and he rates her poorly. Aggravated, Chizuru lambastes him for his shameless hypocrisy, revealing her true pert and hot-tempered self. This one-sided exchange is cut short, however, when Kazuya finds out that his grandmother has collapsed.
They dash toward the hospital and find Kazuya's grandmother already in good condition. Baffled by Chizuru's presence, she asks who this girl might be. On impulse, Kazuya promptly declares that they are lovers, forcing Chizuru to play the part. But with Kazuya still hung up on his previous relationship with Mami, how long can this difficult client and reluctant rental girlfriend keep up their act?
(Source: MyAnimeList)
~~ Adapted from the manga series “Kanojo, Okarishimasu” (彼女、お借りします) by Miyajima Reiji (宮島礼吏).