Once Upon a Demon's Heart by K.M. Moronova (Cruel Fates #1)

This is no fairytale—It’s yearning and guilt of two burdened hearts that will leave readers breathless.

Alira, a devoted demigod knight, has found herself trapped in the throes of a brutal curse. A time loop in which the demon kingdom’s Blood Knight kills her every time. She is haunted by the attack she led on the innocent village of Thornhall, and her guilt consumes her from the inside out. After the twentieth time loop, she has finally had enough. Something has to change, lest she die at the Blood Knight’s hand for the rest of time. A choice she hopes she won’t regret—one to end the war between demigods and demons. Alira is shocked when she realizes that she’s marrying the very knight who has slain her so many times.

A daughter of Venus and a duke of demons. Their love is both cursed and destined—a marriage to save the fragility of their kingdoms.

Kalel is as cruel as they come. A devourer who survives on the gilded blood of demigods. He wants to hate her as much as he did when Thornhall fell, but he finds himself warring with his heart over his emotions for her. Together, they unravel the truths of Faultore, that perhaps not everything is as it seems. The gods may be pulling more strings than they should.

It’s not a question of what love can conquer; it is a matter of what they are prepared to demolish in the path of it.