I feel your pain! My live-in boyfriend eats like a 5 yr. old (no offense to 5-yr. olds!) - mac & cheese, chicken fingers, peanut butter & jelly, potato chips, spaghetti, sugared cereals. He will not touch anything green - no kidding, NO VEGGIES, ever. The only fruit he'll eat is a banana. And he snacks every night on cookies, candy bars or ice cream.
So, what I do is "every man for himself" in the kitchen. He knows he is always welcome to try anything that I'm making. Usually he makes his own. We trade choosing the restaurants when we go out to eat. I try to pick a place where I know I can get something fairly healthy. He goes for places like Steak n' Shake, IHOP, or Taco Bell. We grocery shop together once a week. I can't tell him he can't get what he likes - he lives here too and he pays half the grocery bill just like me. (But it does get real hard sometimes trying to ignore all his snacks in the cupboards.)
He knows losing weight is important to me, but in the past 6 years he's seen me start and abandon several plans...so he probably just thinks, well, here we go again, let's see how long she sticks to it this time. I actually can't blame him for that.
He never fluctuates a pound one way of the other, despite his horrible diet. He says he loves me just the size I am, and he will continue to love me no matter what size I may become, whether it's bigger or smaller. Of course, with our size difference (I'm 5'9" and 199, he's 5'5" and 140) I could whomp his *** if I needed to, so it's not all bad!