Nice to see you again Roz. Lovely piece, and as someone who was married four times, I found it very relatable.
You marry someone for a reason(s) and even if things go sour those things still exist in them. With the stress of "being married" removed sometimes you can be friends again.
My first wife got pregnant by her "boyfriend", told me she wanted a divorce, moved in with him (he left his wife), and broke up with him. All within six months.
I was with her when she had the baby. Two years later I went to her wedding when she remarried. When I moved out of the state we parted on good terms.
It's good to see someone you loved be happy.