Don't think that he will change; he most likely won't.

I was in an abusive relationship and I understand when you say he is like two different people. My BF was that way too and it was very confusing because I do believe he really loved me and was often kind and supportive BUT the abuse got worse after it started despite trying to help him change by therapy and later by filing assault charges and getting a restraining order.

Please end this relationship. I am sorry he had a difficult upbringing but that doesn't make it okay for him to abuse you. It doesn't make it okay and it isn't going to change.