I'm a long term mono secondary so I can't fully relate to his wife. Sage on here is a great source from her perspective though. That being said...have maximum patience. I know it is frustrating but you have to push yourself beyond the norm to give her space and let her find her way in this.
This won't sound very nice but I am coming from some experience so please don't take this personally - Don't forget she is giving you a gift, you are taking something from her. At least that is how she is likely perceiving it. From my perspective as the person who entered into a relationship with a married woman, I felt this way too. Redpepper's husband gave me a gift just as she gave me the gift of her love. I offered nothing in return but the difference is that he is also poly so he thinks differently than a monogamous partner. There is something in being poly for both of them. There is very little to create that type of compersion in a mono/poly relationship.
Give space, be patient, don't push. If she can be healthy and happy in this than you will see the rewards in time.
Playing the Game of Life with Monopoly rules.
Monogamy might just be in my genes
Poly Events All Over