Why do you think this time is permanent? If she has done this multiple times to you, chances are very high that she will return again and again. A good predictor of future behavior is past behavior. Thing is, the outcome at the end, will be the same each time. Your ex has a disorder that compels her to repeat this god awful behavior.
I second this. It's a the script of their lives. Not being whole people with secure identities, they read and act what was written for them in their childhoods. As IMF said, it compels them. They are driven by it, and take us with them when whenever we are with them, with all of the predictable accidents along the way.