Helping him know I'm not them

So my Boyfriend of 2 years comes from an emotionally abusive family. His dad is an alcoholic and the rest of his family just plays along with the horrible things his dad says so he wont turn on them. My boyfriend is an amazingly sweet guy and I love him, but he is always hiding when he is struggling. He has even gone as far as lying about his job so that i don't think less of him or leave him. His dad constantly brings me into their arguments saying that I'll never stay with a guy like him and continuously brings up the time i broke up with him 8 years ago. How do i get him to understand that his dad is just an asshole and that I have no intentions of leaving or hurting him. I tell him all the time and I have even told his dad off a few times for bringing me into his bull.