idk , it seems like she likes you. Although , i could be wrong. Don't let her string you along though.
Try to talk to other girls and go on dates and enjoy your life etc. If this bothers her then she definitely likes you , i think. She has a boyfriend ,so therefore , you are not doing anything wrong. Also , you have told her that you like her so the ball is kinda in her court. But you are still friends, that's the main point.
If you date other girls and she gets jealous, then you can ask her why? OR, she will initiate the conversation with you, if she wants a relationship with you,she will say it or you will now be in a situation to discuss it together ( kinda harsh on the other guy though). I think your current situation is that she has options, her boyfriend and you . You only have her, you like her very much.
If you manage to date other girls that you like, YOU have options. If she maintains the status quo , then fair enough. But now , you won't feel as bad because your attention is focused on someone who you like and who likes you back , rather than someone who MAY OR MAY NOT like you in that way , for sure. The only problem is , if you date other girls, then she may stop being as flirty as she is. Anyway , i think that you will probably in a better position this way.
Good luck