'Crescendo' by Becca Fitzpatrick, book 2 in Hush, Hush series

Synopsis 

Nora Grey hasn’t completely gotten over the recent turn of events in her life. Angels are real, she’s falling in love with her new guardian, Patch, and she’s the descendant of a Nephilim. The last two weeks of her life with Patch have been magical, and she hopes that it’ll never end. But nothing is ever that easy. Someone is still trying to kill Nora, and Patch is becoming more distant. The ultimate kick in the heartstrings is when Patch starts spending more time with Marcie, the girl that has been making Nora’s life Hell for years.