Welcome to the forum. I am sure that you will be receiving posts from many of the other members with advice, comments
and suggestions. First of all, whether you are dealing with
a psychopath, a narcissist or a sociopath the reality is grim and disheartening. It is wonderful that you have a therapist and I would encourage you to continue going. However, if you feel that your therapist has a skewed viewpoint you may want to entertain the thought of finding a new one. Or, if you had only previously gone to therapy with your partner you should, perhaps, go by yourself to be able to discuss the situation from a different perspective.
None of us, in reality, can make the decision for you whether or not you should stay in the relationship or leave.
Nor can we tell you exactly how to leave someone. That is something that we must all arrive at on our own time. For many of us our lives only got better and more clear once we left our P's (psychopaths)....no contact, that is. I have read articles and posts from people that have stayed in long-term relationships with their P's.....but not many, mind you.
One thing that occurred to me is that many of us find ourselves acting differently when we are in contact with our P's. You may want to explore this angle with your therapist as to how it relates and contributes to your own bipolar disorder, mood swings, etc.... There may very well be a connection.