Ok, this is pretty much like LJBF problem in reverse.

So, there's a girl I really like. We started as fuckbuddies (first date almost straight to sex), and I'm fucking some other women too, but as I got to know her better I think she's pretty much what I would like my ltr to be.

The thing is she sees me as a fuckbuddy only, and while she wants to see me and fuck me as often as the can, she sometimes mentions that I'm fun for now and she loves fucking me, but someday she will get a "proper" boyfriend. Very understandable from her point of view, as I haven't been keeping myself exclusive to her. She doesn't date or fuck anybody except me right now - from what she told me she tried dating some guys before meeting me, but she felt no attraction to those "nice" guys.

I'm not 100% sure I want to turn her into a girlfriend yet, I want to have this option. I obviously cannot turn into Mr Nice Guy all of the sudden, nor would I want to as it would destroy the wonderful dynamic that exists between us. I've never had this problem before, what do I do about it?