Wait i'm sorta confused. The doc told him not to eat and he is eating? Or the doc told him to eat and he is not?
Sorry, post again with this and I will try my best to respond.
However, if he has bulimia, lkike I said he needs to know you are there for him. No matter what. If he told you he has an ed, he is reaching out for help. It is your duty to reach back for him, encourage him to lead a happier life.
Good luck with thius and keep me posted on how he is. I hope you are ok.