Hush, Hush (Hush, Hush Saga Series #1) by Becca Fitzpatrick

Nora finds forbidden love with her fallen angel, in the first in the New York Times bestselling Hush, Hush saga. For Nora Grey, romance was not part of the plan. She's never been particularly attracted to the boys at her school, no matter how much her best friend, Vee, pushes them at her. Not until Patch came along. With his easy smile and eyes that seem to see inside her, Nora is drawn to him against her better judgment. But after a series of terrifying encounters, Nora's not sure who to trust. Patch seems to be everywhere she is, and to know more about her than her closest friends. She can't decide whether she should fall into his arms or run and hide. And when she tries to seek some answers, she finds herself near a truth that is way more unsettling than anything Patch makes her feel. For Nora is right in the middle of an ancient battle between the immortal and those that have fallen - and, when it comes to choosing sides, the wrong choice will cost her life.