You sound exactly like the guy I was seeing at work. I'm not a horrible person but I did the same as this girl you were seeing. I was enjoying seeing this guy at work but he suddenly became all clingy and to full on. I could tell that he liked me more then I liked him so I went all cold on him. I just wasn't ready for a relationship as I got hurt by my previous b/f and had been single for 1.5 years and was enjoying it.
Anyway, the guy from work persisted with me continually and he was/is such the nicest guy I met. I'm ashamed to say I messed him around for weeks but eventually I broke it off.... and then I realised that I missed him. We are together now and I'm happy.
I think you should ask her where you stand and just be honest with her about your feelings.