I was Here by Gayle Forman

This characteristically powerful novel follows eighteen-year-old Cody Reynolds in the months following her best friend's shocking suicide.
As Cody numbly searches for answers as to why Meg took her own life, she begins a journey of self-discovery which takes her to a terrifying precipice, and forces her to question not only her relationship with the Meg she thought she knew, but her own understanding of life, love, death and forgiveness.