Honestly, with all due respect, I call bullshit.
If you wanted to end up with her then other women would have ZERO appeal to you.
I think you don't know WHAT you want (no harm there, that is part of life).
You sound like you want a fuck buddy and there ain't nuthin wrong with that, however, you can not ask a woman to step back from what she THINKS is a committed relationship to fuck buddies with the promise that MAYBE you will want to commit to her later on.
A man will NEVER respect a fuck buddy the way that he would a woman that he wants to elevate to the status of life partner. Why should he? If she allows herself to be treated that way then he will never EVER see her any other way then just as the cow who gave away the milk for free. If she is happy with being viewed that way by a man who *supposedly* respects her, then that is good for her too.... no?
Just be honest with her and tell her straight up the way you told us here, "I do want to be with you longterm someday but NOT NOW. NOW I just want to fuck you when we are both up for it but then WE CAN BOTH fuck other people when we really don't feel like fucking one another or when the thought of fucking someone else is more appealing to either one of us."
^^^ Dunno bout you, but that wouldn't sound appealing to a woman who wanted more than *just fucking* from her man. If she IS down for that, then as I said - YOU BOTH WIN.
I mean, she gets to view the relationship through the same eyes, doesn't she?