Adultery is nothing new. Throughout the ages men (with the complicity of women) have tried to justify sex outside of marriage, sometimes even to legalize it.
The history of humanity is highlighted by our inability to get along with each other. The primary focus of the Fifth Commandment teaches the importance of learning to respect others.
The 10 commandments were given by God at Mt Sinai, but the Bible shows that these same commandments were known and in effect long before Moses or a people known as the Jews existed...