Hello Dinbravo,
I don't think there has to be a mental illness or mental health issue/diagnosis for someone to be nasty or deceptive. People with BPD for example often have difficulty in having a relationship at all. Sounds to me that you need to put this whole thing in the 'learnt from experience' box and move on.
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Pegasus
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“Everybody is a genius. But if you judge a fish by it's ability to climb a tree, it will live it's whole life believing that it is stupid.” - Albert Einstein