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Here's your work: "it makes me so angry inside that he has no compassion for my parents". Let him be. You are trying to make him act differently, just as he would like your parents to act differently. His fear of your debt - if it makes him afraid and angry, let him be so, but it's HIS fear and anger, and you don't have to react to it. Don't run away from it; just acknowledge it and let him know he is heard and you empathise with his pain.
By taking this centered, non-reactive position, you will change the entire dynamic. Arguments go zig-zag-zig-zag along well-worn paths; by changing one response a teeny bit, you can make the entire conversation go off into previously untrod depths of communication.