I think it was me. After 9 years together, hubby suggested joining adult swinger sites, to which I declined several times. Finally around 11 year mark, I decided I was ready to give it a try. We have been open for the past 3 and are celebrating our 14th anniversary next week.
We tried to play together, but it was extremely hard for us to find a compatible bi male. I told him I felt secure enough for him to go off on his own, but he had to give me the same option. Initially, his male protective instincts kicked in and he expressed some concern that as a woman, I wouldn't be able to control my emotions. That set me off big time because as it turns out, he is way more emotional than I am. You have to be wired to keep things in check. Not many are, and it's even harder to have a couple than can do that.
It takes trial and error to do it. It can make or break your relationship, but you don't know until you try. You have to work out as much as you together can before you start. How will your partner react to jealousy? Are you willing to stop or take breaks when needed? Are you going to just have different partners, completely NSA (riskier) or would it be ok if you had a dedicated friend who respects your primary relationship?
To do it successfully, you have to redefine your view of the 'traditional' marriage or relationship. If you cling to that, it won't work. Someone will get hurt, you will fight, etc.. We basically had to let go of all we were taught growing up and make our marriage work for us.