We Don't Live Here Anymore (movie, 2004)

Married couple Jack and Terry Linden are experiencing a difficult period in their relationship. When Jack decides to step outside the marriage, he becomes involved with Edith, who happens to be the wife of his best friend and colleague, Hank Evans. Learning of their partners' infidelity, Terry and Hank engage in their own extramarital affair together. Now, both marriages and friendships are on the brink of collapse.