Hello,
Just wanted to give you my perspective. My wife and I are just like you guys, my wife plays with other women, but mostly other men. My wife only does this because it is my fantasy and I have told her that it is a huge turn on for me. My wife and I have been together for 10 years and married for 5 years, and she has slept with 1 other woman and 2 other guys in front of me since we have been married. We couldn't be more happy or in love with each other. We both love and respect each other, and treat these times as crazy adventures. My wife was reluctant at first I think because she may have thought I would be jealous or resentful, but over time she has realized this is not the case and has not changed the way I feel about her one bit, except for maybe feeling more in love with her.
I think you guys just need to talk, a lot, and have real, honest discussions about what you want and expect. Also agree to cut it off at any point and hold no grudges if it goes bad. Agree that it is an adventure and neither of you know how it will turn out until you do it. You have to, in the end, agree to love and respect each other at all times!!