Tearful Eyes ~Anata Shika Inai~

Main character meet a girl on the hill behind the school. She lies on the hill wearing a white dress instead of uniform. He only dares to talk to her after becoming festival committee member, and they seem to have much in common, but she asks to keep white dress in secret. However, after becoming friends, protagonist starts to notice strange shadows behind the girl personality. One day she stops talking to him...

[From vndbreview]