What should I do with the girl I like?

Soooo...

I really feel like crap right now.

The last weekend I went to a nightclub with some friends and the girl that I had crush with was there. That was a really awesome night, she and I danced together the whole time and I was felling in the sky. After that night I was sure that I wanted to be with her, but it was all downhill after that. I tried talking to her on facebook but she never kept the conversation going. At that point I had no idea whatsoever about her feelings, and I saw posts on her facebook that both encouraged me and discouraged me from thinking about her, so I'm really like wtf is going on. Today, I noticed she has been talking to my friend, which she met that night, so I'm like really loosing it. I was thinking to tell her what I felt for her and really don't care what happened after that, like if she liked me too then cool, but if not, then most likely we won't be talking again. I really need to know directly if she's into me, what should I do?