Are there people out there who only want their ex back once they see them doing better?

I keep reading stores about girls&guys who leave their ex partner for someone else then a few months later their ex gets into better shape or is making more money then they want them back. Is this really a thing? Do they actually miss the ex or only want them back because they are doing better
Are there people out there who only want their ex back once they see them doing better?
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