What is going on with this girl?

I invited a girl over to my house in one of those rare instances where absolutely nobody else is home except me. We're both 18. I had met this girl at a party once and we had only spoken through instant messaging for about 2 days before that.

As soon as she came over she hugged me really tight. I thought she was just being friendly, so I hugged her back just as tight and then we were stuck in that hug for a while. For some reason we instantly went to my room and we had sex. I won't go into detail, but she ended up doing everything I like and I actually felt like more than a piece of meat unlike past experiences I've had with girls.

So afterwards I cooked her dinner but it didn't stop, she was all over me while I was cooking, deliberately distracting me. However she soon left due to some sort of family problems (nothing serious but again, I won't go into detail). After she left, I realized I hadn't felt so wanted or needed. She told me I was "bad for her" because she couldn't keep her hands off of me which I liked a lot.

However throughout the week I've tried talking to her, but she's seemed less than interested. She has since told me that just because we did it doesn't mean I should stop sleeping with other girls, but now I no longer want to because I have a crush on her.

Is it possible that she's trying to show me her disinterest by trying to redirect me towards somebody else? Is she trying to hide her feelings? What is happening and why have I fallen for her so quickly?