Request #556 From Gina

Hello! I have been bothered every time I remember a book I read but I cannot for the life of me remember the name of the book! I know the major part I remember is a girl and a friend who is a boy are BFF and then something happens and he gets mad at her and they split up. Then the friend decides he is going to shoot up the school. The main girl hides under a table in the library during the incident. I also remember her going to his moms house and I think looking at a scrap book or something??