If your not happy, then you need to realize that stringing this girl along isnt good for her neither. Before you get too much into the relationship, you need to be honest with her.

Its hurting her and you if you continue this relationship. 2 years from now, you will be miserable and she will not have a clue more then likely. And then, it will be REALLY hard.

Find the strength within you to be honest, open and also firm with her. Just say (to her face) things are not working out and Im sorry.

Its ok. Move on