Establish a boundary in terms of what you will not accept in terms of her dating and leave it at that. Tell her that if she cannot respect that, then she has to finish filing the paperwork.
She's taking her cake and eating it too. She's using you as a "backup" in case none of her other relationships work.
Let me put it to you this way. If there were a girl you wanted to date, would you want her to still go out with you if you weren't the first, second or even third choice?
The main thing you have to get back from her is RESPECT. That is what you are teaching your child. The idea that parents should RESPECT one another first and foremost.
M-43 W-40 2D - 9 and 5
Emotion, yet peace. Ignorance, yet knowledge. Passion, yet serenity. Chaos, yet harmony. Death, yet a new life.