Stay ever... ~Yakusoku Nante Dekinai~

Protagonist has a less than lover more than friend Naho, and their parents get remarried making them siblings-in-law. Girl suddenly falls ill and starts to gradually lose memory. She confesses to protagonist in the end, but the scene is seen by the mother that forces protagonist to move out.

A year later protagonist receives a call from his father saying that Naho died. Time that stopped a year ago starts to move again.

[From vndbreview]