It sounds like she is a very selfish person who does not notice the damage she does to other people. There is no diagnosis for this in general. She concerns herself with her own needs and situations that benefit her with no regard for others. In psychology we call this narcissism. This is the ability to be completely self centered and concentrate on yourself. Narcissists are unable to take others into account in making decisions - it is all about them. The fact that she would have sex with this man and cut her children out of their father's life is hateful. What about the kids? They are impossible to treat and often bring the selfishness into therapy. Hopefully her children will be able to consider the rights of others. I would keep my distance.
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