Jorge Sanz in "Amantes" aka "Lovers: A True Story" (1991)

 Synopsis from IMDB

Set in 1950's Spain, a young man leaves the army and looks for a job so he and his fiancée can get married. He rents a room from a widow, and shortly begins a torrid affair with her. The fiancée figures it out and decides to win him back by offering herself to him and taking him to meet her family. Ultimately he has to make a decision. Based on a true story.