Why would a girl talk about you so much but when I asked her out it changed?

So last spring i sat next to this girl in this class. We knew each other but not that well but anyway we talked a lot nothing serious just a lot small talk and after a couple of months I start getting people telling about how she talks about me all the time. Next thing I know she is acting really friendly and laughing at just about anything that I say even if I wasn't trying to be funny. She would say weird things like what do u do after school and telling me that she tells her family about my stories, she even invited herself to my house on the last day of school. I figured it was that she liked me or she thought we were really good friends which didn't make a lot sense because we didn't know each other very well before this. I've never really been the ladies man so this was kind of a new experience for me so I just played it off and I really didnt make it obvious that I liked her back. We talked a lot over the summer through message I even said we should go see a movie with our friends. Again I never really made it obvious that I liked her. Then the school year and we were in the same class again but this one and she still would say som ackward things. She would stare at me too. Homecoming came and some of her friends were telling that I should go because she wanted to dance with me. I figured this was a good chance to talk to her. I went and she seemed pretty excited about it. At the end I talked to her and then got interrupted by this kid. I ended up just straight up asking her out which was probably not the right move. Suprisingly she said yes. After that it pretty much went downhill. We would small talk afterschool and she didn't seem that interested in talking to me. It didn't last long she eventually told me that she wanted to go back to being just friends. After that I didn't really know wut to do I tried to talk to her but she didn't want to talk about so I pretty much have quit talking to her and she has tried to talk to me that much either. I guess the real question is how did fall apart that fast? and what did I do that screwed it up? and do u think there is any legitimate chance of it getting started up again? I know u gotta move on and Ive been tryin to just kinda ignore it but it keeps bothering me and I really don't feel like talkin to people I know because I'm kinda embarressed about the situation so Id thought Id ask random people on the internet.Why would a girl talk about you so much but when I asked her out it changed?
well first off you liked her and talked to her alot and then she decided to be a ***** and do this to you, and unless your leaving something out, it honestly sounds like you didnt do ****. so you have to move on. really be friends if thats what you want but as a girlfriend forget it. unless she shows intrest in you FORGET IT, in fact talking to other girls might make her really jealous if she likes you *hint hint*