Agree.
My take is
@Free_Agent the reason you're having difficultly extricating yourself is because in all likelihood you're addicted to the sex. I have been there myself with one of my long term ex's.
It's a serious addiction and if you don't kick it, it has the potential to destroy you.
As stated almost ad nauseum, this girl is a liar. She enjoys all the trips and other perks you offer, as well as she enjoys the perks her ex offers her as they've taken a few trips together as well, fully funded by him.
My guess is she is playing him as well.
I have a very strong sense she is taking the upcoming trip with him.
I wouldn't even confront her about it, there is no reason to think she would be honest as she has lied to you previously.
Take whatever is left of your self-respect, wish her well and walk.
I really hope you do that. This entire thread saddens me to no end, how one woman has the power to affect a man's mental processes in such a profound way.
Good luck mate.