thats a really awkward situation maybe you could arrange a night out/in just the two of you and talk, have a few drinks, watch a movie or whatever it is your into and just be honest with her, tell her that you know what you did wasnt nice in the first place and remind her how much she didnt like it, and also how you tried to right your wrong. then just say that you feel she was doing the same thing to you then and is now using you and you dont think its fair,
Just remmeber while you are saying this stuff to her say it in the most gentle,nice, and Non-threathning way other wise she will get defensive and feel as though she is being attacked. remind her constantly throught the conversation that you love her/would hate not to be friends etc etc etc.
you really have to approach this subject very gently and be really nice to her as she is probably already feeling rejected by this bf of hers...
i know this will not be a nice conversation to have but if you dont get this off your chest it will end up turning into something much worse.
Good luck, let us know what happens