Kawaii Watashi no Anata

Itsuki lost his grandmother, his only immediate relative, when he was a baby. For the 23 years since then, he has been living in a dilapidated apartment with Mizuki, who is 16 years his senior. Itsuki has been suppressing his unrequited love for Mizuki since his childhood, thinking this parent-and-child relationship would continue forever. However, the apartment complex will be demolished soon, and the danger of their cohabitation coming to an end is looming...

(Source: Libre, translated)