I read a book which I think was called "Open". It had a wedding ring on the cover, and it was a biography of a woman and the transition she and her husband made from monogamous to open to meet her needs.
I was struggling, trying to adapt to my husband's call for change.. I found The Ethical Slut very difficult to read, and though I appreciated Tristan Taormino's writing, the biographical style helped me to understand another point of view emotionally in a way I hadn't expected.
I wish you and your partner all the best.