Meghan, I was there when my W moved out. I stayed kind of distant, not actively helping, and not hovering, but I was there. It was one of the hardest things I've ever done. Like you said, someone has to leave first, and since I was staying, that meant that she had to leave on her terms, not me leaving because of her terms. Whether it was the smart or the right thing to do, I don't know, but if I had to do it again, I think I'd do the same.
As for what was said, W just said "We'll get through this. Both of us." And I simply smiled, said "goodbye", gave her a kiss on the forehead, and went in the house.
Stay strong, we're all behind you.
Me: 28 W: 28 Together: 9.5 years Married: 4 years Bomb dropped and W moved out: 6/15/14