Her Warrior King by Michelle Willingham

He was given a choice—wed a Norman bride or watch his people die. King Patrick agreed to wed the daughter of his enemy to save the lives of his people — though he swore he would never bed her. Yet Isabel de Godred has no intention of being cast aside by her new Irish husband… She tries to make the best of her marriage and find a place for herself among the MacEgans. But the tribe refuses to accept her as their queen, and neither will her proud warrior king. Despite Patrick’s vow of celibacy, there is no denying the forbidden desire rising between them when they are alone. For if he dares to love Isabel, he risks his very throne…