Hi, I'd like to help you with your question.
I am sorry you are going through this with your ex partner. Oftentimes, it is very difficult to break off a relationship. It is even more difficult when one partner was abusive and continues to try to keep the relationship going, even after it's over.
First, I think that you were very strong to break off such a relationship. What occurs when a partner is abusive and violent is that they also use emotional abuse to keep their partner in the relationship. It is a difficult and often confusing situation to remove yourself from and I believe that is what you are experiencing right now. However, the fact that you were strong enough to end the relationship is a very good sign.
The best option in this type of relationship is to break off contact completely. The issue with still maintaining contact, even just occasional or through something like email, is that the abusive partner only sees the contact as an opportunity to continue the abuse. They will accept any avenue they can to continue the manipulation and control of their victim. Your partner will use a variety of emotional triggers including guilt, shame and promises of better behavior to get you to stay and accept the abuse.
I highly recommend that you seek out counseling. If you can, find a therapist who has experience with abusive relationships. You need to gain self confidence and increase your self esteem so that you can emotionally remove yourself from your relationship with your partner.
There are also some books that can help you. One is called The Courage to Be Yourself: A Woman's Guide to Emotional Strength and Self-Esteem by Sue Patton Thoele. Another is Why Does He Do That?: Inside the Minds of Angry and Controlling Men by Lundy Bancroft and one more is It's My Life Now: Starting Over After an Abusive Relationship or Domestic Violence, 2nd Edition by Meg Kennedy Dugan and Roger R. Hock. These are all available on Amazon.com or your local library or bookstore may have them as well.
I hope this has helped you,