HELP-what do I do with this great girl?

She is never going to know how you feel if you do not tell her. You don't have to come right out and say " I really like you and want you to break up with your boyfriend." But you can say things like " I hope your bf knows how special you are and how lucky he is to have you." This will open her eyes to things that she might not be noticing. You defiantly want to stay friends with her and see her as often as possible. The more that you interact with her the more that she will see how awesome you are. She may never break up with this guy but if she does she will see that you are a person who has never left her side and will probably realize that she likes you too.