The Kiss of the Sky - The Song of the Sylvan, #1

She thought reclaiming her home was the only thing that mattered- until she met him. Myrthe's mission was simple-infiltrate the dreaded human city and retrieve an artifact that could change the tides of war. As a sylvan-born of the forest-she would do anything to save her people, but when she is caught by an arrogant human mage, her plans spiral out of control. Trapped behind the stone and copper walls of the city, Myrthe has to find a way to obtain her target without giving the mysterious, and enticing, man watching her every move a reason to ensure she never escapes, even if she's beginning to wonder if she wants to leave at all.
Ardin serves the Temple of the Aspectis in the name of finding vengeance, but his powerful magic is slowly killing him. With enemies lurking both within and without the city, the end of his quest is nowhere in sight-until he stumbles upon a woman trying to steal from the temple. Like a spark of bright light in his dim world, she brings a change that may light the way to his future or burn it to ash. This is the first book in the Song of the Sylvan series, an epic fantasy featuring a world conquered by forest and a war between humans and the non-human sylvan people.
Slow burn enemies to lovers from opposite sides of the war.