Forever Immortal by Amelia Hutchins

Isadora MacPherson is having a horrible week. What should have been a simple mission turned out to be a well-laid trap by the Prince of the Hybrids. Held captive, unable to escape his hold or his heated kisses, her entire world is spun from its axis, and everything she’s believed and known is challenged by the egotistical, self-centered, dreamy-eyed monster whose kisses leave her breathless, and his bites leave her craving more.
Cian had one mission. Take out the hunter’s strongest weapon and make her into one he could use against them. What should have been an easy task is anything but simple. Isadora’s blood sings to him, awakening his inner beast who craves her innocent kisses. She’s supposed to be easy to break, but the more he learns of her, the more he craves the beautiful siren that lures him into her murky depths with her sassy mouth and quirky personality.
There’s also a big problem: She’s his mate, the one who awakens the protective beast within him wants nothing more to keep her safe.
When enemies turn into lovers, how far will they be willing to go to test their mating bonds?