I could be wrong, but if I'm not mistaken, your therapist is required to keep your discussions strictly between the two of you. The only exception is when he/she believes you may be a threat to yourself or others. Again though, I'm not at all an expert on the subject.
Why not ask your therapist what they are or are not allowed to divulge to your parents? Why not ask this before telling them about your dad?
At any rate, I think that you should tell your therapist. This is the stuff they are there to help you through. I'm sure your therapist would be happy to help you determine if he is emotionally abusive or not, and how to deal with the situation.