Why do ex gfs get bitter?

Why do girls break up with a guy , complain about him, and reject him every time the guy tries to win her back. But when the guy finally gives up and meets another woman that he genuinely loves , the old girlfriend gets bitter and wants to try and get his attention again and make him forget about his new girl. But If she can’t get his attention again she gets BITTER AND MAD? Why do girls do that?
Why do ex gfs get bitter?
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