You need to talk to a student counsellor and get this sorted. meanwhile, consider this: does the fact that he uses your answers affect anything? If it doesn't, let him do what he wants. If your classwork is assessed lower than you feel is right because of your partner, then you need to bring this up with the person in charge of the subject, overall.
Sounds like your teacher is a bit rubbish, but she won't be the first or last so don't let it get you down.