Most Helpful Girl
Women want to believe that they are irreplaceable and if your ex moves on quick he's pretty well proving that's not true. Plus, even if she doesn't want you anymore, she doesn't want anyone ELSE to have you either. She wants you to be at home and miserable like she is. It's an ego stroke.
My fiance's ex said to him, "Good like trying to replace me but I bet it's not going to happen! And go ahead and talk to 'so and so (some girl)', she ain't got sh*t on me!" There's that sh*tty attitude that a lot of women tend to own. She had no idea he'd meet me within the year and we'd be engaged after 8 months :)
I don't work this way, I know that there are plenty of worthy women out there that would be good partners. I've never had someone move on quick after me so I can't say I'm familiar with this pain. I take a long time to move on, after both my LTR (one of 4 years and another of 3 years) it took me at least 6 months and working through some pretty severe depression before I finally had the sun on my face again.