Ohhh ladies. I think most of us have this problem with the men in our lives. I'm with Smisen-- for me, my boyfriend just hasn't got a clue what's healthy. He'll make us a "healthy" dinner of an entire box of pasta, with a POUND of ground beef. Meat and carbs and the occasional bag of chips. The boy diet.
I can totally relate to it being frustrating watching your boyfriend eat an entire box of cereal.. yummy SUGARY cereal that it would be awfully nice if you could eat too without having to worry about your waistline...! Sadly, as I am trying desperately to learn... my boyfriend's eating habits should have very little correlation to my own. His metabolism is better, his body's not a fan of packing on fat for childbirth, and he plays football (...well, soccer, but he's Irish) 3-4 times a week and comes home sweaty-faced and spent... and I... don't.
It's hard, and I'm not one to talk, beacuse I'm dealing with this right now... but there comes a time where you have to focus on yourself. Your own habits, your own body, your own efforts, your own health.
And then of course analyze why you're upset. Are you upset because you're genuinely concerned for his health, and the horrible sugars and chemicals he's putting into his body? Or are ya just kinda envious that he can eat an entire box of cereal and not wind up in a guilt-ridden fit of tears? (That's where I'd be!)