I wish I could be more help, but I'm struggling with the a similar concept, in that I'm just lost when it comes to things like what you said happen. I had been im'ing a girl from school, and sometimes she just doesn't respond, and most of the time I think she's just not interested. I don't even know what to do anymore, I feel like giving up, but it's so hard to let go.

I say do not give up though, maybe she's going through something, or really busy. It's very ambiguous, and you don't know for sure what's going on until you ask her or find out someway. Has she not responded to you like this before? If not, then I'd probably just chill out and talk to her next time and not worry about it.