Kirai na Aitsu ni Sukaretai

Masato Kashiwagi got dumped by his girlfriend in college for another man called Kizaki by not being a good boyfriend. Afterwards he decided to become a "rental boyfriend" and he ended up becoming one of the most popular rental boyfriends. The story begins when he is rented out to none other than Kizaki.

(Source: natalie.mu, translated)