I'm going to try and explain how I see it. I've been a dumper in the past so i know what it's like being the one who walked away. I went through a small phase of stupidity when my ex and I broke up. My ego is bigger than i thought.
Lets put it this way. when you're a dumper, you feel invincible. You have a feeling that you're attractive enough that someone else would come along very quickly. hence, this is the reason that women do most of the dumping. you feel great for awhile. You really do. Could be days, weeks or even months.
But something strange happens one day when you no longer have that feeling. All of a sudden, you start feeling like you're missing something. It just doesn't make much sense. then, all of a sudden, you see your ex. And the weirdest thing happens. you start peaking into her life and wonder what she's up to. May not necessarily care about them but curiosity drives you to check up on them. At that point, you might to be friends or just to say hi. And the only thing that can work is when you start to miss her. That is when the walk away start to feel nostalgic.
But if the walk away never gets to go through that and continues to see how right she is for walking away, she will never get to experience that. In her mind, all she thinks is "wow, I'm glad i got rid of that loser."
do you get it? When a woman wants to leave you, she wants to leave you because she feels suffocated or thinks that someone else is better than you. The exact same way you would feel if you want to walk away from the woman because you feel that someone else might be better.
when she realizes how great things were when you were together, how much she misses you, then and only then will she see the foolish beat of her heart in wanting out.