Christinastar,
How did you find XFs depakote? Did he tell u, were they out or did u go snooping? You don't have to answer this, just look at your behavior.
Nonetheless, it does make a little more sense that XF might have dual diagnosis with some of his cruel and almost baiting treatment that you have described. There are some book recommendations and mental health sections here on SR that might help you see you are not crazy and part of BPD is this sudden jerking between love and dismissal. I think due to abandonment issues. But understanding a piece of his problem doesn't mean you can fix him.
My concern here is u have a son with an A/BPD so you can't entirely go no contact. Previous advice to get your stuff and your car remain good steps. Start truly treating this relationship as an X. Take his lead in the matter. He is going to keep moving on and rubbing your nose in it for sure.
Sometimes I am stronger when I act as a mother. Do this for your son so you can set up a Normie haven for him now while he is still small.