hard for me

I went camping with some friends for the weekend as i do a few times a year and this time, one of my friends brought his sister with him. I met her once a while ago and found her to be touchy feely and kind of flirtatious, but in a short time she was to be closer to me and i found it easily comfortable to be closer to her. We were in more physical contact with each other and flirting. The next day we walked off and kissed, she wanted to look into my eyes during that time. Walking back, she told me not to let her brother know because he might get mad. At the end of the weekend, as hiding what we did, we kind of walked away from each other. We didn't give each other our numbers and i started to think it was just a fling of passion and she isn't as interested in me as i am to her. She lives far away and i feel a horrible feeling i am going to miss something to important. She had an effect on me i never felt before, before we even became close. but i hardly know her at all. what do i do?

You said shes one of your friends sisters so wouldnt you have his number? why dont you learn about her through him?
She might be just be out for attention, i.e. horny.
Dont rely on her to do the hooking back up with you though, if you want her you need to go get her.

Some women are coquettish by nature. I wouldn't read much into her actions. I knew a girl who would sit on my lap in the presence of her boyfriend. I felt bad for him, and, in a way, for her. She must have been attention-starved, either by her parents or by her boyfriend.

However, if you still desire her, you should do the legwork and go into it without high expectations.

You know how many other girls are going to manipulate you this way? Don't worry you are not missing out on anything. You stay a "nice guy" and I guarantee this will happen on a regular basis ;P