Shadow of the Heart.

Twins Watit and Ruth lead completely different lives. Watit belongs to high society in the city, while Ruth leads a modest life in the countryside. When Watit gets severely injured, their father asks Ruth to take over his brothers life, pretending to be Watit in hope of finding the person who tried to kill his brother. Metinee, is Watits fiance. Their engagement is based on a business deal, not affection. When Ruth replaces his brother, Metinee doesn't notice and marries him. Metinee gradually begins to realize that he is a different man, while slowly falling in love.