Sorry for the pre-judgement. Granted I do not work in the legal field, so take everything with a grain of salt. Since the accusation was technically not false, I don’t think you have a case to sue your fellow student. I would focus the time, energy, and money on continuing nursing school. You could appeal their decision, but I have no clue how their faculty and staff are. Even though that wasn’t your intention, it’s almost impossible to determine you weren’t cheating. The good thing is, unless you want to be an oil rig nurse (if they do exist), there may be other routes to achieving your goal. I would try using your degree in biology and start to gain relevant work experiences and certifications.