How do I get out of an emotionally abusive relationship?

Abuse. Seek help with a mental health professional who can help you terminate the relationship but most importantly can help you understand how you entered a self destructive relationship so you don't repeat a self defeating pattern. Best.
Get help. And support. Enlist the help and support of friends and family. See a therapist. Involve the police and the legal system. Do it now.
Call for guidance. The National Domestic Violence (and yes, this includes emotional abuse) can help: 1-800-799-SAFE (7233).
Talk. Be open and honest with your boyfriend about your feelings, your thoughts, your fears, and ask questions. You might be assuming things. Honesty and communication is a critical part of making a relationship last.