thats good that your family are supportive. my mum is amzing and so understanding. she didnt really get it at first but she does now. I think it must be a hard thing to understand unless you have been through it or known someone who has.
do you think you could chat to your boyfreind and suggest ways he could help you? he probably really wishes he could but like you said, doesnt know how. I used to write my mum letters telling her how i felt and suggested ways she could help. sometimes that can be helpful and easier than talking.
this is hard and i know what you mean about getting back on track then it knocks you down, but you can do this. you have taken a great step in posting on here and that takes courage often, just to ask for help.
i struggle with body image and fighting those thoughts so much also but i find this website really helpful-
http://www.hungertorecover.com/recoveryselfhelp.htm
it has different coping strategies and how to fight those negative thoughts. it may help you a little.
do keep posting and remember that you deserve help and to get well.x