Hi,
It sounds like you are in a hard situation. I would tell, I think, cause there doesn't seem to be another way out of this.
This person is sexually abusing you. In no way is this a consensual relationship. Blackmailing someone for sex is abuse and a crime. It is even worse that it is someone who is supposed to be lawabiding and protective of others.
Please stay safe and take care of yourself. You deserve to be safe. I hope that this will soon be resolved.
Kate