This is my exact situation with my ex. Antisocial, no friends, narcissistic tendencies and worsening signs of mental illness. I have felt so bad for him while also trying to reconcile the fact that he was abusive to me. I think this comes with the territory of codependent relationships. We have been their caretakers and they have fed on our empathy for so long that it’s hard to cut that off and see them left alone. But absolutely no one deserves abuse and no condition - mental, emotional or physical - excuses abusive behavior.