Haru Tsuzuru, Sakura Saku Kono Heya de

The final diary written with you. On the day they entered university, Haruki and Sakura had a fateful encounter in the classroom. Charmed by each other, they lived together after graduation, but their separation came suddenly. Sakura had disappeared from the world. Since then it's been five years, five cherry blossom seasons. Still brokenhearted, Haruki happens to find a diary. It was the yet-unfinished ten-year diary that Sakura had been keeping. (Source: Square Enix, translated)