Leave Me Behind by K. M. Moronova

Nell Gallows is the sole survivor of an elite dark forces squad, Riøt, after a detrimental attack two years ago. Unsurprisingly, she’s being put up as the top candidate for the special ops team: Malum. The squad that goes where no one else will or can. There’s only one problem: Malum blames their one casualty from the Patagonia mission on the Riøt squad.
So what is she to do when she finds herself on a plane to California and on her way to a sure death sentence? A one-night stand. At least, that’s all it was supposed to be—one last night to be free. Only, she finds out too late that the dark and mysterious man she solely wanted as a fling is not only her new comrade but also the one she dreaded meeting most—her immediate superior and untouchable devil in the field. Bones.
He’s hell on earth—cruel and unforgiving, but most of all, he hates her, and he makes sure she knows it. And yet, she finds herself unwilling to leave his side when he’s unable to get to the evac point when their mission goes awry.
She stays behind with the devil and the secrets he keeps. They only have one another to trust when no faith is left.