My so wants me to do extreme fasting

I was talking to my so the other day and he said he wishes my belly was a little smaller. I have had issues with self image and eating in the past so this really hurt me. I told him if he isn't happy with me that he should look for a different partner. He said he was happy and loved my body the way it was. Well an hour or so after he said that we got into an argument. I mentioned how I feel about myself and he said that I should just fast. And that I should only drink water. I figured fine I'll try it since I haven't been eating much lately anyway. Well today he said that I need to not eat anything until June 1 and then not until June 5 and then not until the 10.... I was just stunned at him saying that. I know it's not healthy to do that especially with having starved myself in the past. When I told him I didn't want to he got upset with me. How can I make him understand how I'm feeling and why I don't want to do this.... He is so stubborn and I'm afraid that this will be the end of our relationship, but I won't let myself suffer like I did for someone else.