OT times were ruled by Kings and Judges, they set things in order as they saw fit. Some sought God but yet turned away from the law and commandments of God. When Christ came, believers were charged with the commandments, one being, thou shall not commit adultry. If you consider the word adultry and it's meaning, you'll find your answer.<quoted text>
There is no verse in the NT banning polygamy. How could something be right in god's eyes at one point, but not the other point
Christ once said, If you love me, you'll keep my commandments.