I have, and the easiest way to deal with it is to realize that staying with someone that you don't want to be with a worse thing to do then just to leave.In time they will get over it. If you lie to them or are not honest then you will just be leading them on, letting them grow more and more attached to you and hurting them worse. It is always best to honest about your feelings, even if that hurts someone. Don't feel guilty about it.
I have. Not that I'm proud of it. Because the guy was honestly the SWEETEST guy ever. He would show up at school everyday with flowers. When I ignored him, he would have his friends give them to me. I feel really bad looking back on it now.