I am sorry but you need to leave him. No guy is worth being treated like that. Being underweight is not a good thing. He needs to be healthy himself before he can judge anyone else. He has no right to treat you like that. That is abusive. It is not physical but it is emotional and mentally abusive. You should never put up with that. You are setting yourself up to end up with an eating disorder because of it. You have a choice to make though either stay and have your self-esteem broken down or leave and gain self worth.