Hey Millhouse,
It's really great that your feelings are bottoming out and allowing you the strength to begin making decisions and assessments about the situation; you deserve a pat on the back for that right now.
I do think you are correct in the assumption that she thinks she can have you back at any time she chooses; in my opinion only I would be telling her that she knows where the door is and not to let it hit her on the butt as she leaves.
Block her number on your phone and start living. Let her deal with her guilt her way and not use you to cleanse her of it so that she can nick off again and enjoy the next week until she feels the need for forgiving angain when she runs back to you to give you the next installment of her wonderfull new life. She is torturing you and enjoying it, it seems.
Good luck with this Millhouse...
Rhian