D - Wow. I am speechless. You have hit the nail right on the head here.
I also belive that something triggered them to open their marriage. In the beginning, I believed (and was led to believe) that it was just because, after being together so long, things got complacent, stagnant, loss of passion, boredom set in. But as I peel away the layers, I realized there is more to it. And what you just stated is the same conclusion I have come to.
But I tread lightly. I don't want to violate their privacy. I listen quietly and offer love and comfort as he has started to open up. I pass no judgement.
It's a tricky situation for everyone.
As I said before, I love him and want what is best for him. I know that he loves me and that he does love her deeply and I accept that. His compassion and ability to love is what has drawn me to him. Asking him to change that would mean asking him to change himself and I don't want that. I love him the way he is...... I just miss him alot in the time we don't spend together and wish that it could be more frequent. All I can do is ask.