I would be cautious about assuming this unless they have actually been diagnosed by a psychiatrist.
It’s not actually true that the Cluster B disorders are “almost always impossible to treat.” DBT therapy has had success with treating Borderline Personality Disorder.
The other two are more difficult to treat. It’s possible to treat Antisocial Personality Disorder if treatment begins in childhood, though I don’t know offhand what the success rates are. And Narcissistic Personality Disorder is notoriously hard to treat, mostly because the person who has it can’t understand that they have a problem.
It concerns me that so many people nowadays assume that their partners/family members have a Cluster B disorder, when these people could have any number of problems, from a neurological disorder to drinking too much to just being an over controlling asshole.
Anyway, someone doesn’t have to be mentally ill to be abusive. Abuse is mostly about controlling the other person.
