It's hard but she did have a boyfriend and so things could never really have started up. Its not right to interfere in other peoples relationships and she probably was flattered that you like her (most girls would be) but the fact she has a boyfriend prevented anything from happening, and it doesnt seem that she wanted to break up with him. It was a tricky situation, but the best outcome is to move on from her. It may feel like you're never going to meet anyone special, but i promise you that you will. It takes time, and if you go looking you rarely ever find her. Just be patient, have fun and she will come along in her own time, and you will be glad you waited