wmpd- unfortunately it sounds like he is very focused. I think the best thing you can do is support all the wonderful things about him that have nothing to do with size or body. When he does something sweet for your, remind him of his kindness, when he comes up with a smart solution, praise his cleverness, when he makes you laugh, dont forget to let him know how great it feels to laugh and be happy with him.
...and thats all you can do. You cant make him want to get better. (I know you know that) Remember to keep yourself well, too.
Please take care.