What should i do (relationship)?

im having a relationship with an undergraduate girl im instructing, im a gta at the UM minneapolis,, anyways,, she is also now taking a may course with me and we broke up,,,,yahhhh, we made a tape that makes me look really bad and she's threatening to release it to the cl on youtube or something unless i give her an A for no work, and keep screwing around with her whenever she wants,,,,i could get fired and most probably someone would figure it out,, what should i do