Except Wes that your argument is too simple (not saying you are, just the argument, I think you're fascinating).
I have moved away from Andy several times. Whenever I do, the nastiest starts up. He might not be in my bed anymore, messing with my mind in that way, but he affects me even more by being mean and since 3 of the kids live with him, he has the power and the ability to do that OFTEN. As he said once, 'If we can't be friends I have to hate you', but for my sanity I CAN'T be friends. I would always want more, even 20 years down the line. He would have to let go of his notion of friendship but whenever we try just civil, the nastiest resumes. It's been 4 years so I have no reason to believe that if we're separated for life, that would ever change.
There are also few M's like your first M where the couple drift apart, remain amicable and are mutally happy at the arrangement. Most M's the couple separate because they fight, or mis-communicate, but instead of fighting in the kitchen, after D they just carry on fighting on the phone, fighting in the street.
That's exactly what happened in my case, and even if all goes quiet for a few weeks or even months, sooner or later there will be another fight. We have fought more D than we ever did in the M. Counterproductive D, in my opinion, given his reason.
Also, my aromatherapist friend still has on and off problems with her XH, despite being engaged to a new H-to-be. He will come in the house uninvited and be all chatty with her, in front of new hubby, who then gets angry, and my friend is caught in the middle.
There's my other friend who can barely mention her XH without sounding contemptous, even though the split was her decision, and he never saw their 2 sons again (his choice) after their D. It's been 8 years since she saw him last. The cost to her sons is not knowing their real father.
Statistics have shown that 2nd, 3rd, 4th marriages don't work, usually, because then you have to add other people into your already complicated family dynamic. In my case, I wanted to rip the OW's breasts off, I felt such rage. I know I would still feel like this in 10 years time.
My experience of OW, also, is that they feel as much rage as me, so there's all this bitching, back stabbing and power struggles going on.
Even after the trauma has died down, no one I know speaks fondly of their X's new wife. No one. At best you can just pretend to ignore it.
Then you have to take on someone else's children and they might be resentful towards you, or you might not want to, or the man might have a V and then you are unable to have a baby with him, and it's a natural urge to want to give birth to the baby of the man you're in love with.
If I re-married, I'd want my own family with that man, not a ready made one. Very few men would do that since I already had a family with Andy. Very few men would want to if they had kids with XW.
There are a whole mydraid of reasons why you are bound to First partner, and I personally believe that a D paper and not having sex, does not separate you from that person, and most people don't even think of that when they D.