My Partner's Negative Body Image is Affecting Me

my partner has been commenting on his weight lately and it’s been bothering me a lot. he mentioned wanting to start wearing a binder again because he saw himself today and feels fat. i don’t know how to support him in this. i tell him that i love his body so much. and that he’s so handsome and attractive. i don’t think he believes me. he’s talked about being chubbier as a kid and hating it, and in his adult life, he’s been skinny. but since getting sober, not so much. his words. i’m worried about him:( i have an ED and it kind of triggers me that he talks down on himself in this way, and it makes me worried that he will develop an ED from his low self esteem. how can i support him and help him feel better?