The Seven Year Hitch(2012)

Jennifer and Kevin are childhood best friends who have lived together, platonically, as adults for many years. When Jennifer decides to marry her cheating, manipulative boyfriend, Bryce Kevin has to stop the wedding to protect her from making, what he believes is, a terrible mistake. With a little help from his brother and neighbor Kevin discovers that he and Jennifer are already legally married due to common law, having lived together for seven years and, as such, Jennifer can not marry Bryce.