The Endless War by Danielle L. Jensen

THREE LIFE-CHANGING CHOICES, TWO STAR-CROSSED LOVERS, AND ONE UNCLAIMED DESTINY . . .

Newly crowned as king of Maridrina, Keris watches powerless as his forbidden relationship with Zarrah is exposed.
He knows there is only one way to save her when she is imprisoned by the Empress: to ally with the kingdom he nearly destroyed.
Zarrah, held captive on the dreaded Devil’s Island, faces two choices: regain the favour of the Empress who condemned her or die a traitor by her royal command.
But dare Zarrah seek a third path: a rebellion to overthrow tyranny entwined with a destiny she must fight to claim.

Facing impossible odds, Keris and Zarrah must somehow find their way back to each other, before it’s too late . . .