Yahoo Web Search

Anna and Will were each other's first: first kiss, first love and first and only relationship. Now, 10 years in, as Will is about to propose, the couple's best friend makes a drunken toast, suggesting that they should sleep around before their inevitable marriage. The joke lands like a lead balloon, but the thought lingers until Anna proposes that they try opening their relationship as a sexual experiment. Together, they venture out of the purely monogamous boundaries of their relationship. Wikipedia