Emerald Desire (Emerald Trilogy) by Lynette Vinet

The rebel heart… As wild and beautiful as the Irish countryside, Dera Brennan knew from the first that Quint Flannery was the only man she would ever love. Ignoring her family’s warnings, she gave herself to Quint with passionate abandon. He was hers and hers alone until she found him in another woman’s arms. To spite her faithless lover, Dera impetuously married Lord Fairfax, an imperious English aristocrat, and Quints enemy. Yet even separated from Quint by a vast chasm of wealth and privilege, Dera yearned for his hungry, punishing kisses. Not even the cold brilliance of diamonds could quench a desire burning with emerald-bright intensity.