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I know from experience that it is hard to convince some people that you need to be a veg*n. My parents were very unsupportive but one day I decided that I would tell them. I figured, it's my choice, and it's not like they can force me to eat anything. It didn't go too well for me because now I have to cook my own meals and buy my own food, but I know some people will be more understanding. Just try to have a calm conversation with him and explain why you feel this way. I hope it works out.