In religious sense marriage is the legal form of contract or agreement between man and woman in which both of them agree in front of the society concerned. So it is something annouced in legal terms and not hidden. No one can object on that becasue both agree and one way or the other it is announced that they can now have the legal relationship from that point on.

So there cannot be comparison of getting married more thab once and having a casual relationships without any commitment , they are very different. In summary marriage is very different to casual relashionship even if man married more once as mentioned.Even if his act may not be perfect but no one can say that any such has broken the rules of morality.