Adultery has NEVER been sanctioned by the Lord.
Plural was an ordinance that was sanctioning in the scriptures you can not erase that, and from the pattern in the scripture it happens with each new dispensation.
That's not the half of it!
According to the Mormon scholar Todd Compton, in this LIST of Joseph's 33 plural wives:
Joseph also repeatedly lied about his sexual practices. And the last time I checked, the LORD had some rather harsh things to say about bearing false witness.