Move on and take care of yourself and your niece. Your ex is just boomeranging herself back into your life due to the fact that things are not going pretty in her life and she has returned back to use you as an emotional crutch. Do yourself a favor and go back to living in the moment. It’s the same situation with food, if you are trying to lose weight and then you eat a big piece of cake or have fast food then how do you feel afterwards, disappointed and depressed. It’s the same thing only this time be strong and maintain no contact. If you maintain no contact, hopefully she will get the message and search for another victim.
Thank you and take care
-AP85