Just let it go. Who the heck cares about what happened last time and the time before and the time before that.
Eventually it reaches a point and when people have had enough and they leave for good. Bad relationships do eventually end and one person will decide they want out and end it for good and despite what they may have said in the past.
You should have been the one to reach the point of no return and given she appears to be the one to have led you the dance and pissed around with your feelings.
But obviously you lack self esteem, confidence, maybe are afraid of being alone, or frightened you will get nobody else and which is why you so desperately try to cling on to her, why you will tolerate her shit. So long as you have someone, you don't care how they treat you...
Snap out of it !!