Through the Fire by Fleur Smith

Their love might stand a chance if he wasn’t bound by duty to kill her. Clay has sworn to destroy any nonhumans. And Evie isn’t human.
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Evie’s father has protected her ever since her mother died in childbirth. For as long as she can remember, he would uproot their lives and move across the country at whim. Two years ago, Clay, a student at the latest in a long line of schools, changed her life forever. Through Clay, she discovered the truth about herself, and the reason behind her father’s fears. Now, Clay is back–battle-scarred and mysterious. Despite being as attracted to each other as ever, they are trapped on opposite sides of a war with no end in sight. Caught between what her heart wants and what her head knows, something has to give. What will Evie choose? And what price will she have to pay to claim it?