There’s a shoujo tragedy I’m looking for: there’s this couple in highschool and they...

There’s a shoujo tragedy I’m looking for: there’s this couple in highschool and they were very in love but out of nowhere the guy breaks(he might not have broken up with her he might have just left) up with the girl and left for like 1-2 years(I don’t remember) and then he comes back and they are together again and the girl falls in love with him again but she finds out that he’s sick and really only has that year with him before he dies. Anyway he dies and she’s sad but graduates normally. She and the guy would always write messages to each other on a bulletin board in their school and she saw that he left her on last message