We've been telling you to kick her borderlined personalitied ass to the curb this whole thread so why would you think anything different then you are doing the right thing? This is ending exactly how it normally ends. Its not a surpise.
He gives her something you can't give her... He makes her miserable and that is all she knows and that's all that makes her comfortable. If she does get with you, she will be soon looking for someone behind your back as well because she's addicted to drama.
Good luck in your new job. Forget her and learn a lesson in that you should immediately distance yourself emotionally and physically from any woman who is already taken. you now suffer from your own poor Karma. Sorry dude. Learn the lesson and you'll heal quicker.
“The willingness to accept responsibility for one’s own life is the source from which self-respect springs.” ~Joan Didion