About 20 years ago, when we both were 18 until we were 29, my girlfriend was exactly as OP described. I also stood by her throught all those years. She was (is) the nicest and most lovable girl until she got mad. Then all hell breaks loose, with verbal and physical violence included. After almost 10 years, I knew I had had enough and moved on. Fortunately that was around the time I moved to DR so I could avoid further drama and death threats. I lost count of how many psychologist, psychiatrist and therapies she went to. Nothing worked. We still talk from time to time. She got a degree in psychology a few years ago, even though she knew she could not treat herself, but she says at least she could understand where all those episodes come from. The violence has not stopped, and by now she all but stopped trying to have a relationship with men.
OP, run and move on. That's the only thing I can tell you, if only because I don't know any better.
OP, run and move on. That's the only thing I can tell you, if only because I don't know any better.