We Were Liars by e. lockhart

Cadence and her mother spend every summer with her cousins and families and the boy she loves on their private island off Massachusetts.  But Cadence cannot remember her fifteenth summer there and is suffering from terrible headaches and depression.  When she goes back for her seventeenth summer, all is changed and she struggles to remember why. When she does, it’s devastating for her - and for the reader!  This book packs a huge punch and will stick with you long after you finish reading. 

Mrs. Turnquist