Does having sex with a girl have to mean everything? Can't it be just casual?

I recently had sex with this girl and I just met her a few hours prior. The thing is she seems to really like me but I just don't want to get involved but instead of leading her on I spread out the talking times so it's like once a week. She is mad because I am not committing and won't give her my full attention. Does this make me a bad person?

Please don't say I should have told her my intentions before we did it because that's kind of a double standard - she could have easily said she wanted more...