As revealed as way back as post #16.
I see it more like the fact that we tend to remember our "first great love" (not so much the second or third, or fourth, you ever notice?), scientists don't know exactly why, but believe it has to do with "imprinting" on our brains. That can put him (her first love) a bit on a pedestal to begin with.
It happens in the case you mentioned, that they guy became successful, for all she knows (we don't know if he's that happy behind the closed doors and fantasizing daily about his long ago pot smoking 19 y.o. chickie) and compared to the way her life turned out, it seems the dream.
So maybe it's more like only when her life soured in comparison to her perception of his, did she feel she dumped what could've been her great catch. She wasn't feeling that pain previosly to that when she was happy in her career and relationship. (Yet it's a fantasy, because who knows HOW it really would've worked out, if at all, if she had stayed with him).
Also fellas, did you notice how the woman in this story blamed the guy for the relationship not working out ("because he was very driven and determined at the time") but absolved herself with excuses ("I was much younger than him, straight out of school and did not know what or who I was").
Also, did you notice how she turns a virtue into a fault by saying his trait of ambition was what made her break up with him? IOW, he was busy making something of himself, and she probably wanted him to give that up to spend more time with her. Of course, his ambition ultimately made him "mega rich", which she feels she missed out on. The very thing she claims she didn't like about him, is the thing she now likes about him. This is why you cannot ever abort your life purpose because some women whines about it (though you musn't let her feel neglected).
One more thing I'd like to point out: the fact that she feels she missed out on the better life. When we read threads about how to move on, and some of us write the thing to do is be indifferent and having a great life is the best revenge, some other guys wonder, how does having a better life act as revenge on someone who was indifferent enough to dump you? And here we see the answer to that: even though she was the one to feel 'I reject this man' and dumped him accordingly, this woman yet looks back and sees what she missed out on - and that's what gets her to feel the regret. On top of that, there's that extra bonus little twinge of pain/guilt that she keeps in the back of her head, haunting her, that says, "And you, chickie, you would've stopped him from becoming successful. You're a curse. Your own marriage failed. Everything you touch turns to crap".