Nubes de verano / Summer Clouds (2004)

Daniel (Roberto Enríquez), Ana (Natalia Millán), and their little boy, Manuel (Kevin Almodóvar), travel from Madrid to a resort on the Costa Brava for the summer. Ana runs into Marta (Irene Montalà of L'Auberge Espagnole), a local shopgirl whom she's met on previous visits. Marta introduces Ana to her cousin, Robert (David Selvas), who runs an antique shop. Robert is immediately attracted to Ana. Marta tells him that Ana is happily married, and confesses that she has a crush on Ana's husband, Daniel. Robert, intrigued, makes a pact with Marta. Robert will help Marta seduce Daniel if she will help Robert seduce Ana. One night, the cousins cunningly arrange to separate the couple, and some serious flirtation ensues. While Marta, casually dates a local surfer, Tomás (Roger Casamajor), begins to have second thoughts, Robert grows more obsessed with the couple. He befriends Daniel and peppers him with questions about the strength of his nine-year marriage. Robert also asks if Daniel is attracted to Marta. "Fidelity's another word for laziness," he tells Daniel. He visits Ana and surprises her with a goodbye kiss. As the summer wears on, his machinations begin to have an effect on the couple's stability.

Imdb