My friends don't understand my eating disorder?

I was trying to talk to one of my closest friends about it. I can usually tell him everything and he will have something to say or an answer to my problems.

So this time, I tried to discuss my eating disorder. Something he blatantly mocks everyday at lunch and makes a joke about it to his friends. Usually it’s something around the neighborhood of me giving part of my lunch to someone else and then they feel bad because of how small my lunch is and he will usually state, “She doesn’t care. She only eats the 100 Calorie packs anyway. She even counts out her chips to match the serving size!”

But I thought I could tell him. And so I was explaining to him that I’m always hungry it’s just really difficult for me to get the courage to eat. That it started because I’m tall enough to be a model but there are models that are taller and skinnier than me. So he said, “Why even compare yourself to a woman that probably gags up every meal after she eats it? That’s not beauty.”
But I’m a photographer and so I said, “I know, but average looking girls don’t look as good on camera.”

And then he started mocking me about how fat I am. I’m 5’8’’ 127 lbs.

And then he was like, “You know…just shut up if you’re going to go on about how beautiful models are and how every girl should look like that.”

And so I did.

But why don’t they understand? I try to fix it everyday but I can’t. They just make jokes about it. All of my friends; not just him.