Mosquita muerta (2007)

Marcelo and Sofía love each other, but both suspect the other of infidelity. Marcelo, a film director, accidentally discovers condoms in Sofía’s purse. They are really for Marcelo’s younger sister, but he thinks the discovery confirms his suspicions and keeps one as evidence. Sofía discovers the condom in Marcelo’s wallet and takes for granted that he is cheating on her. Pepe, Marcelo’s cousin, pretends to be him to impress a girl, further complicating the mix up.