IMHO what he needs to understand is that dealing with an eating disorder and quitting smoking are two totally different things. i know because i have dealt with both (and still struggle with both).
smoking is an addiction to a substance. it's an addiction not a disorder. some people can quit cold turkey, some people need help like support groups or the patch etc. it has nothing to do with being a strong or weak person. everyone starts smoking and quits for different reasons and in different ways.
eating disorders are typically an emotional/psychological issue (as i'm sure you already know). he should not assume that unhealthy eating habits are the same as an addiction. virtually no one can just wake up one morning and QUIT having an eating disorder.
unfortunately you may never be able to convince him that he's wrong. the key is for you to keep working at it, get the help you need, and don't let his negative and incorrect opinions affect your progress. like a previous post says, try and get him to go to therapy with you, but even if he won't - don't give up! find a friend or family member in your life that you can confide in about your struggles and get your support from that person instead of from him.
btw i don't mean to downplay how much it sucks that he's not supportive - because he should be the one person to love you and support you through any struggle. i'm really sorry

hang in there