I understand your predicament. While it is true that you are not compatible, she will hold your feel to the fire, force you to say what you cannot prove, deny it, and make you out to be the bad person.
Tell her that you feel that there is more to her life than she lets on, and even if you are wrong, you nevertheless are uncomfortable in the relationship and it gives you too much stress.
You are not compatible because you are a more settled person and she seems to be more a party animal, and you are looking for some more like yourself.
You don't have to worry about hurting her feelings. She seems to be a pretty resilient person with a lot of resources and men waiting in the wings.
You just don't want to be one of them.
I understand that you feel you will lose an argument with her and you probably will. She is a manipulative person, and perhaps even a narcissist, which means that she can manipulate others, win over others, and may not care how others feel. That is a great advange to have in that kind of a lifetyle but it does not make true happiness.
BotXXXXX XXXXXne: tell her that he relationship is too stressful for you and you are no longer happy being in it. She cannot argue happness. If she tries tell her that you know that the relationship will not last and you are done trying.
She will not let you off the hook easily if she is a narcissist. She will not like to lose her control over you. It is control she wants, however, along with admiration. She can get all she wants without you, and she will.
If you want to go into great detail and learn a lot about women (and men) like her, then get this book. Everyone sould own it.
There is a chance that she is not a narcissist, by rather has bipolar disorder and is often involved in a series of reckless sexual adventures.
Either way, she is not the girl with whom you will live happily ever after.
The most important thing is to maintain control of the conversation and don't let her take you where SHE wants to go. Don't give her foodholds. If you want to be out of the relationship then tell her you are done.
You will have to find your way in this conversation. If you want to break up, then do it. You may not succeed the first time. She is probably very tough mided and can bend your wil. Do you best to be strong.