Here was me driving around listening to the radio and what did I learn? Well, apparently monogamy is 'so yesterday'. There was an extraordinary interview with two couples one married, one engaged who all live together. He loves her but she also is in love with and sleeping with her and she is in love with the other man who isn't her husband (who also happens to be gay and sleeps with other men). Follow all that? Well done you. It's called being 'polyamorous' (in the Oxford dictionary from 2006) or perhaps to use the Bible's 'so yesterday' terminology 'consensually adulterous'.
A very extreme yet interesting take on contemporary sexual ethics. You can listen to Monogamy and the Rule of Love and do read How does a polyamorous relationship between four people work?.