Seeing Other People (2004)
Ed and Alice live together and will soon marry. She decides she'd like more sexual experiences before settling down with the man she loves, so she convinces Ed they should "see other people" (as in, sex with strangers), even as they continue to live together and plan the wedding. They discuss it. Each knows someone who thinks this idea is cool; each has a friend who thinks they're nuts. Things start reasonably well, but soon their relationship goes awry. Can the genie get back in the bottle and Ed and Alice return to companionship - or does seeing other people put an end to how Alice and Ed used to be?