From the Erfolgtraurigkeit Files

The opposite of schadenfreude rears its head again, this time when your ex finally decides to get his act together after you break up:

I was happy for him, but there was also a little teensy part of me that felt whatever the opposite of schadenfreude is—instead of feeling happy at someone’s misfortune, I felt resentful at someone’s good fortune. Why couldn’t he have gotten his proverbial shit together while we were dating? And, a more uncomfortable thought: Was it somehow my fault? Maybe, I realized, I had seen him as someone who had potential but just needed a little tweaking. But it was sort of annoying that he managed to do all the tweaking after we’d broken up.
...
[It] hews to a common pattern, in which the woman, seeing the man as a project, tries to “improve” him, thereby leading to resentment in the relationship when the woman feels that the man is not improving enough, and the man feels emasculated and condescended to.

See also penultamours.