Infidelity. The Montbryce Legacy Anniversary Edition, #9

Once bitten, twice shy. Betrayed by his late first wife, Gallien will never give his heart to a woman again; however, he has a duty to remarry and sire heirs for the Montbryce earldom. Peridotte has long fancied herself married to a handsome Angevin nobleman. She fears the cold, arrogant Norman to whom she finds herself betrothed when political intrigue forces them into an arranged marriage. Afraid to admit their growing feelings for each other, they appear doomed to a life of resentment and unrequited love.
But there's a more insidious, hidden threat that could cost Peridotte her life.