Secret affair from a memoir

Raz, a 20-year-old teenager has been assigned to babysit one of her father's friend's daughter, where she finds a memoir. Slowly she starts to read the memoir against her morals. Every part of the memoir slowly connects her with her own life. She sets out to find the narrator of the story midway through the memoir without finding how the narrator's life ended. With her own personal problems with her best friend and wanting to find out the narrator, her journey takes an unexpected twist leading to revealing the unexpected truth of life.