I'm going to chime in here with a few sentences. This is what life experience has taught me. Whoever came up with the idea that we are supposed to stay with and in love with the SAME person for our entire lives must have been CRAZY. Somewhere along the line things get boring for one or the other. People " fall out " of love.
How many marriages go 50-60 years without straying ? That's human nature. But outright open marriages are bull****. The stray cat usually comes back home. Make it work or walk. Life is to short.