Criswell, Jill. Frozen sun saga #3

Sequel to: Kingdom of ice & bone

To save her lover's life, Lira of Stone swore allegiance to a demigod known as the Dragon, and was transformed into his weapon: the Dragon's deathbringer. She uses her gifts to conquer nations and unleash demons... and must find a way to free herself before he declares war against the gods. After the warrior Reyker Lagorsson attempted to overthrow the Dragon, Reyker's soul was fractured. Now a shadow of his former self, his battle-madness grows stronger by the day. He will stop at nothing to kill the Dragon. Lira and Reyker face off as enemies. But can a god like the Dragon be killed? And if so, at what cost? -- adapted from jacket

"[The] final installment of the Frozen Sun Saga" -- jacket