Yasashiku Koroshite, Boku no Kokoro wo.

Although only 19 years old, using his good looks and his body as a weapon, Nao Kanzaki is a natural gigolo. Being stabbed after a breakup, he is saved by a refined and dangerous man who is a Yakuza—Ryouichi Murou, boss of the Ichinose-group. Stopping Nao from leaving the city after his wounds have healed, Murou brings him to his apartment and offers him a deal in order to pay for Nao's treatment. Even though Murou tells him that he's "not interested in brats," he's contradicting his words when he starts kissing Nao like a lover. What will happen to Nao who swears by himself that he definitely won't fall in love...? (Source: Gentosha Comics, translated)