Chant2012,
Your description of your experience is both horrifying and heartbreaking. I hope that you are able to get into therapy to help you deal with the trauma you've suffered. Do not be too hard on yourself about going back to him or clinging to the relationships. Trauma bonds are incredibly difficult to break, and breaking them takes constant mindfulness of your emotional triggers and control over your reactions.
Also, from what you've written, I think your ex's problems go beyond NPD. I think you might be right about sociopathy/psychopathy.