Just to expand on the polyamory - Many people in loving marriages, have different rules about exclusivity... In fact some might argue, that it is the open relationship componants that strengthens the marriage:
People who identify as polyamorous typically reject the view that sexual and relational exclusivity are necessary for deep, committed, long-term*loving relationships. Those who are open to, or emotionally suited for, polyamory may embark on a polyamorous relationship when single or already in a*monogamous*or*open relationship.*Sex*is not necessarily a primary focus in polyamorous relationships, which commonly consist of people seeking to build long-term relationships with more than one person on mutually agreeable grounds, with sex as only one aspect of their relationships. In practice, polyamorous relationships are highly varied and individualized according to those participating. For many, such relationships are ideally built upon*values*of trust,*loyalty, the*negotiation*of*boundaries, and compersion, as well as overcomingjealousy, possessiveness, and the rejection of restrictive cultural standards.
http://en.m.wikipedia.org/wiki/Polyamory