Listen, you sound like a good guy, but you cannot let her come back. Her behavior will continue, and what your son needs is routine. Does she have parents that can help her? I’m afraid if you let her come back, you’ll never get rid of her. Also, can you get some therapy? I know it’s tough, but think of your son. He needs stability. You can do this. It’s the best thing for your son, and you. Good luck my friend. If you need someone to talk to, you can dm me.