Tough situation. I understand you wanting to ask for advice because it seemed like you already tried to ask her or talk to her about this but felt confused by her answer or like you didn't word your question correctly.

I encourage you to try again, maybe say youve been wondering what non exclusive means to her. Sex only? Just friends? More serious or potential for more serious but not monogamous? And ideally what type and what frequency of physical affection she's looking for at this stage? She might not know or have an answer and may just want to "go with the flow". That's an acceptable way to respond and you should just consider if you're OK with that.

"is my need for physical affection legitimate"

Yes

"can i ask for it"

Yes, but I've found it can be helpful to make sure you're asking in a way that is open ended or gives the other person an easy out

"and, if it cant be met, should i end things"

If you want. I feel like the main reason would be so you can devote your energy to something else. If you're not having trouble managing your energy and time though? You might want to keep it open ended and then just date others instead to fill the void you are missing with this person. Maybe you'd be less horny if you had another hookup in your rolladex or whatever

"can i end something that was never that ‘serious’?"

Of course. You can even say something that acknowledges the lack of seriousness.