Wings of the Wicked by Courtney Allison Moulton
She's been warned of the dangers. But she'll be betrayed. Balancing real life with the responsibility of being Heaven's warrior is harder than Ellie ever imagined. Her relationship with Will has become all business, though they long for each other. When Cadan comes to her with information of Bastian's new plan to destroy Ellie's soul and to unleash war against all of humanity, she fights to stay ahead of the reapers, even as the revelations of those closest to her awaken a dark power within Ellie that threatens to destroy everything-including herself. Treachery comes even from those whom she loves, and Ellie is broken by the deaths of those who stood beside her in this Heavenly war. Still, she must find a way to save the world, herself, and her love for Will. If she fails, there will be hell to pay.