Robert, Katee. Dark Olympus series.

Sequel to: Neon gods

"When her family executed a coup that dethroned Zeus himself, Psyche knew she was in trouble, but she wasn't prepared for Aphrodite to demand her literal heart as payment. Or for Aphrodite's gorgeous son to be the one determined to strike the blow"--

Psyche knew she'd have to face Aphrodite's ire eventually, but she never expected her literal heart to be at stake... or for Aphrodite's gorgeous son to be the one ordered to strike the killing blow. Eros has no problem shedding blood, but when it comes time to take out his latest target he can't do it. Confused by his reaction to Psyche, he does the only thing he can think of to keep her safe: he marries her. As lines blur and loyalties shift, Psyche realizes he might take her heart after all... and she's not sure she can survive the loss. -- adapted from back cover