I'm looking for a shoujo

I posted a while ago, but never got answers lol, but...
There's this one shoujo manga I read a loooong time ago, like 6 ish years ago. I forgot most of the details, but its really sad.
Basically a girl liked a guy, but he is dead (from a sickness maybe). He left her a map (marked with an x) to find his second button for when she graduates- something along those lines. I dont believe she knows he left the button for her. The second button was underneath a tree or bush in a box. They used to meet there before he died. After she finds it, she's happy she found it and hopes he's watching her.
I'm an avid yaoi reader, but this is one of the couple shoujos I've come to grow fond of.
Please help me find it ;-;