11 years ago, I fell in love with one of my swinging partners and she with me. My wife knows her and knows all about our relationship. Our marriage is my top priority, so there is no chance of breakup and realignment. In fact, my relations with the other woman are actually a positive influence in our marriage.
My wife understands that it is quite possible to love more than one person at a time, and since there is no threat to the marriage, she accepts that I have a need for this other woman. She also knows that if she dies, I will buy a one way ticket to this other woman's city.
For quite a while I was seeing another woman for whom I had quite strong feelings, but I think it was not love in the way I love my wife and the woman I mentioned above. She would come to our house, and we would have sex while my wife was out shopping or playing bridge, etc. Then when my wife got home, we would all have lunch together or go for a boat ride or something like that. It was all above board; no sneaking around. That is over now, much to my regret, but the pain of the breakup was not the devastation that I would feel if either of the other two women walked out on me.
It takes a special wife to recognize that these kinds of relationships are not threatening but rather are an unusual kind of need on my part. She would probably prefer that she is the ONLY woman I really care for, but my love for this other woman is such a small part of our wonderful relationship, that she tolerates it quite easily.