Maybe it'd be a good idea to spend some time apart for a while, or at least start hanging out in groups. The more one on one time you spend together, the more her hopes are getting up. If you do end up alone with her, just try not to sit too close, and say goodbye to her like you would any other friend. When you're ready, maybe you should pursue this relationship. I mean, you are clearly very attracted to her, so don't forget to be honest with yourself about feelings. But do wait until you're ready for a relationship.