Why do people become so offensively bitter after a break up?

Anonymous
I've noticed almost every girl I've dated and had a falling with, they turn into complete snobby, condesending people. Like they'd wish I caught an STI or killed off. I understand break ups are hard but does it really make you wish emotional/physical harm or death on the person? I've had a girl I was in a long term relationship with that cheated on me and I still don't wish for her death or harm, I think it's insanely immature and somewhat bad karma for yourself. What gives?
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my first girlfriend was the one who asked me out, she was obsessed with me and always wanted sex. She'd become vulgar whenever I'd pay the smallest amount of attention to another (Not in that way though), she ripped out a patch of my friends hair at a party because she thought she was coming onto me. At that point I felt I couldn't date her, told her we needed to cool it. She goes an tells all her friends I was a lousy lover and loves to play women. nope. then she went and got pregnant the next week
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second

the one I've been in the longest relationship yet, never trusted me from the get go, she always thought I was out with other girls but in reality I never was, in fact at that time I could barely even get girls attention but I guess she saw differently. she cheated on me with her ex, as well as some hot shot from another high school. I broke up iwth her the moment I saw them exchanging sexual remarks on their myspace, which I never knew about. she now claims I'm the one who f***ed her over
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even to this day she still claims she gave me everything and yet she was possibly the worst and most lame liar I've met.
Why do people become so offensively bitter after a break up?
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