I don't think that I can offer the one answer why this happens.
But, in my XW's case, I think she was looking for her next husband as soon as we separated and that it was a matter of security for her. XW never had the best self-esteem.
She dated like a whirlwind for about 9 months. Finally, she met a younger, impressionable guy who is totally submissive to her (from what I can tell) and they moved in together immediately and were married less than a year later.
I think she has convinced herself that this is the real thing, but I've observed enough as an external third party to believe that this is a matter of convenience for her. Will it fall apart? No idea. They may achieve "Till death do us part" for all I know. Truth is, good for her if they do. I just know that I don't have to be in the moment with her anymore. That is liberating.
