WTF has just happened?

Ok bascailly me and this girl were getting really well. We enjoyed each other company and she admitted to liking me and that she never had this feeling since her last boyfriend. She has been fucked around alot with guys just to get into her pants and always ended hurt from it but she said she felt different with me.

So one day i asked her about me and her being offical but she said no and that she isnt ready just yet. I said ok and continue my day then she texted me saying she considers me hers and that she always want me their with her.

This sound good dont they? Well their yesterday she came to my house and we having a good time and things led to sexual things. Half way through it i stopped and asked what was wrong cause she seemed she wasnt enjoying it and simething was in her mind. She told she doesnt want a relationship and left my house just like that. She said she likes to be alone and that she have been having doubts ever since she said she want me their.

For some reason i feel used and i dont know why. I mean she did the deed and then fucked off... she texted me saying sorry and i knew this would be the last time i would ever talk to her so i made it known how i felt and she didnt sound to happy hearing it. Then asked that we could still be friends and i told then and there i would never work out...

Am i justified in the way i acted and could anyone explain to me wtf has happened