Why did he leave me for a bad girl?

My boyfriend left me for a bad girl. Why wsnt i enough for him? I was the good girl career oriented nice respectful, he was pretty much rough and bad and he left me for this bad girl who us bipolar lives pff wellfare does not work and curses at people , emotionally unstable. Why do men like women like that? Why?
Why did he leave me for a bad girl?
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