MIKE - Is it true that Joseph Smith was getting married to other women behind his wife's back?

JOEL - Joesph Smith was sealed to other women as directed in the revelation on plural marriage(D&C 132), but he did not have any traditional husband/wife marital relationships with anyone other than Emma.
Reports of Emma's anger over some of Joseph's sealings to other women have caused some historians to incorrectly assume that she might not have known about every one of them. But there is nothing in the historical records that specifically supports this assumption. The records only indicate that she did not give her consent for every one of them and that she was not happy about them happening.
A verse in the revelation on this practice directed to Emma says:

"And let mine handmaid, Emma Smith, receive all those that have been given unto my servant Joseph" (D&C 132:52).

"All those" does not suggest that she was aware of only a small number of them.
Emma never did completley accept the doctrine of plural marriage, although she tried very hard to. In fact, on some occaisions she actually did give permsision and even chose some of the women for Joseph to be sealed to. But the bottom line is that there is not enough evidence to support the idea that Joseph was doing this behind Emma's back.