Colin,
Run for your life! I know this is an old post, but there is a chance that you might see this. If you let them continue to suck you in, you will be trapped in a hell that is very difficult to escape. I could go on because I have lived it, but you need to search for the terms Narcissist and Psychopath. These people have some sort of radar, and knowledge, conscious or not, that allows them to target the moral or weak persons, using your values against you, and/ or your hurts and wounds being constantly reopened.
Do No Contact, and get help for yourself.
Warning: NEVER do couples therapy with a narcissist. They are even able to make YOU look like the problem to the therapist!!! Nothing like being injured again in what should be a "safe" environment.