Who makes the rule???

Who decides who goes bad? A married couple. Happily living together, having the normal mother raising kid, and daddy making it rain routine, and all of a sudden,he starts to have a side chic, and no body will find it strange or frown upon it. The moment a woman/bad girl decides to have a side guy, people will curse, frown, talk and she will be divorced. So my question is, who made the rule? Who said men can do it and woman can't??