Why would she do this to me? I hope there arent many girls like this.?

I was talking with her for a long time. There was a lot of texting and a lot of flirting. She was giving me so many signs that she was into me that I'm not going to list. Anyway, one day I just decided to tell her that I like her and she said "Aww, well to be honest I like you too." I then decided to ask her out and she said yes. We went out to the park then the movies. She even posted on fb "At the movies with Luis." Luis is me. Some of my friends and family were commenting saying things like "ahaa and who is stacy???" Not her real name. She commented with a ":)".Now many of them have in mind that I am dating her. It turns. Out that the next day out of nowhere she said that she only likes me as a friend. I was crushed. I really fell for her. I never had a girlfriend before and I thought I was on my way and then she does this. Why would she lead me on like this if she knew that I like her? Now I won't know whether to believe if a girl likes me when she shows signs. It's going to be embarrassing to tell all the people this because she basically played me out. What do you think of this?