Prizzi's Honor (1985) on Netflix

In New York, the hit-man Charley Partanna is like a son for his godfather Don Corrado Prizzi, who is a powerful mobster. In a wedding of a member of their family, Charley meets Irene Walker and he falls in love with her. Irene introduces herself as a tax consultant, but indeed she is a killer hired by the Prizzis for a "contract" in New York. They get married, and later Chaley realizes that she betrayed the Prizzis and had stolen their money in a casino. Charley has to face and decide between his code of honor with the Prizzi's family and his love for Irene.