A werid and tricky situation.. Help?

There is this person i dated just once 2 months back. I asked her out for she flirted with me for a long time. I am positive me and her really enjoyed. Then i asked her very shortly after the first date if she would like to go out seriosly. She said she was "kinda seeing someone" and that she would like to casually go out. I took the refusal extremely well and behaved extremely calmly and said it was not a problem. I walked away.We exchanged some emails over the summer. I met her again a few weeks back and she behaved really "nicely" with me. What is all this supposed to mean? Both of us are in the same high school but this sem i got no cles with her. What do i do? I kinda like her still