In Honor Bound (The Chastelayne Trilogy #1)
DeAnna Julie Dodson

Lady Rosalynde stares at her groom on the first night of their arranged marriage. He will not love her? Well, she will love him--and she will win his heart.
But Prince Philip's heart appears to be made of ice. Rosalynde could not possibly know of the festering wound on her husband's soul... how deeply he struggles with the circumstances of his first wife's death. Or what King Robert has done to his own son in trying to preserve the crown.
In ruthless pursuit of the throne, Philip's cousin penetrates the defenses of the castle and captures King Robert. Philip rallies his army, preparing to fight to the end for his throne. But the battle within is greater. He knows he cannot hold his kingdom without divine aid. Yet he has hardened his heart against God. Against forgiving his father's unspeakable offenses. And against the unfailing love of Rosalynde. Can Love reach him before the kingdom is torn from his hands?