I am so sorry you are going through this. I still think you need to weigh the pro and con of being with her. From what you've posted you maybe should have stayed broken up with her and moved on. Is this situation really emotionally and mentally good for your well being? I know I don't know all the facts but you do and you need to make the best choice for you, because she doesn't seem to be as concerned about your needs, wants, feelings than she is about her NRE with that guy and her lust for him.
But again all I've said is based entirely on what you've posted and only you, and trained professionals, know what is right for you.