Why does it hurt so much? And why can't I stop thinking about?

So I have been texting this lady I met on a dating app. I came to know that we went to a same programme and studied in same college. It felt good talking to her and we met for a coffee. I like her and she also said that she want to continue meeting. But then she is now unresponsive. Haven't blocked me but no initiative at all and one word response.

This shouldn't affect me but I feel hut and kinda depressed. It feels dark and lonesome.

What should I do? How do I get over this feeling of being left?