The War Priest by Ann Aguirre

Dour. Dutiful. Dogged.
Personal tragedy drove Callum McRae to join the Order of Saint Casimir fifteen years ago; now he’s in charge of a hold he hasn’t lived in for years. Supplies are scarce, he has no knack for dealing with people, and the Gols are at the gates. To make matters worse, he’s also battling an attraction so powerful and forbidden that it imperils his very soul…

Canny. Cheerful. Charming.
Joss Bristow seems bright and cheerful, but she’s hiding a well of sorrow that fuels her music. She’s also prone to leaping before she looks, exactly how she ends up besieged at Burnt Amber. Though she wanted to get to know Callum better, she never imagined that falling for him could cost her life.

He’s the dark of night, and she’s the sun that shines just for him. Two wounded souls have never needed each other more, but between his holy vows and the devastation of war, the odds are stacked against them…