Trust and communication are the two most important factors in any relationship. Although my husband and I have not had any problems in these areas, we have had a few problems and so have seeked a sexual health counselor. She had recommended a couple books, one of which dealt with Poly and the other with marriage/relationships in general. I highly recommend picking up this second book as it was very eye opening and shares some experiences of other couples on the brink of divorce. The book is titled Passionate Marriage by David Schnarch, PhD.
I know you were not looking for a "what should I do" type of response, but that is all I can contribute and I think this book might be helpful. The way I am seeing your situation though is that if you get a divorce, poly or mono relationships that follow have nothing to do with the divorce itself. Of course if your wife chooses to be a pain or has a serious problem with your chosen lifestyle she could try to get full custody.
Of what you have mentioned about your wife, I sense low self-esteem issues and possibly either a religious or very conservative lifestyle. It is one thing to not view porn oneself but another to tell someone else that they are not allowed to, especially a grown adult. I wonder if this view is due to lifestyle or does she think that you will like these women better and find her not as desirable?
Not sure where this is going so I will just end it here. I wish you and your family luck and hope.
Life is about the journey and not the destination,
so what better way to know life
than to wander all the roads and paths set before you.