His Human Bride by Anne Bordeaux

The Planet Rune-Yon. She’d taken her pleasure when he was in chains. Now Breccon Tallel will have her on his own planet, and on his own terms. Rune-Yon is like nothing Katharine Leigh Parker had ever dreamed of. Twin moons in a purple sky illuminate her lover, Breccon Tallel, as he drives her to the brink time and time again. But Breccon’s people are ailing, and Katharine can help—if she can prove her loyalty.

Pledge her body and soul to Breccon and her allegiance to all Rune-Yonians. Five impossible tasks stand between Katharine and a new forever. Together with her alien mate—touching, kissing, loving—she can do anything. For she is Breccon’s, and Breccon is hers.