My suggestion
I think by now he got your point already,he knows you care for him but he is what he is. Not taking his health condition seriously just like my mom. She doesn't test herself unless i got everything ready for her and usually the reading scares her but after one day she forgets again. I think you should drop the topic for a while because it is not working for him. Start with cooking health meals for Diabetic like bitter melon, switch to brown rice, low GI bread or whole wheat high fiber bread, no sweet treats at home... etc. Oh, and walking and other excise really help lower the blood sugar level. Try a different approach. Good luck with everything.