JV, for now I would probably focus on improving your R. I doubt you'll get anywhere with his eating disorder until you guys are on a better footing. And you can't help him if he leaves.
You can compliment other things about his appearance (or intellect, or sexual prowess ) while trying to avoid getting sucked into talking about his weight. Or, if you think it is a particularly good moment, you can say "honey, I love you fat or thin, but I am terribly worried about your health,because I know bulimia can be a life-threatening disease."
Meanwhile - learn all you can, so you can be prepared when the time does come to tackle it head on. And do try to get him to take a multivitamin and some fish oil capsules (maybe tell him it's for his heart, without mentioning the ED?). If you could also get him to try 5-HTP (5-hydroxytyrptophan - a serotonin precursor that is available as a supplement) - you could tell him it's for weight control (it is sometimes taken for that). If it raised his serotonin levels, that might help with the bulimia in the same way Prozac does.