Why do some girls want a ex back after their new relationship or rebound fails?

pandaking2p12
This is just something I notice some women will hate their ex boyfriend move on really fast then the new relationship failed 8-15 months year then they beg the Ex boyfriend to take them back. Why is this? I had a few girls/friends with benefits do this to me
Why do some girls want a ex back after their new relationship or rebound fails?
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