Tons of great advice already. You must lead by example. You cannot force him to want to change. He's 24, 10 feet tall and bulletproof. You must stay your own course. If you do not, next year you'll be on here trying to lose 20 pounds instead of 10. And he'll be 300 pounds. If he wants to eat junk, make him go buy it. Don't enable him. Also, don't succumb to any pressure from him to eat something not on your plan. If you want some sort of treat plan for it ahead of time and make it a big deal. Work it into your plan and let him see you do it. Good luck.

His habits are influencing yours. They aren't changing them. YOU are allowing them to change.

You can only be responsible for yourself. If he wants to eat poorly, that doesn't mean you have to eat poorly. He will have to decide if he wants to change his own eating and exercise habits. In the meantime, perhaps part of your motivation for eating right and exercising yourself could be to set a silent example for him. Don't criticize him or judge him, but if you want to make healthy decisions for yourself perhaps you will end up influencing him.

In my own relationship, there are times where my diet is so radically restricted that my DH and I prepare separate meals for ourselves. That way he can have what he wants- guilt free- and I can have what I want. Other times we take turns cooking and he cooks one night, I cook the next. Whatever the one cooks, the other eats without complaint. Perhaps when you move in together you can influence him a bit by preparing healthy meals when it's your turn to cook.

After college, I moved back in with my parents and became the resident food preparer of the household in lieu of paying rent. My dad (the only unhealthy eater in the family) lost a fair amount of weight because I just provided healthy meals.

I am a volume eater, and in order to stay within a happy caloric range for myself, I need to really bulk up my meals with vegetables. I put vegetables in absolutely everything I make. Sometimes they're even via puree, shredded or pulverized, but nobody has every complained (my father, ex husband, or toddler), even if they complain about not liking a particular vegetable.

I'm currently dating someone who is incredibly meat-centric and liked to make fun of my produce-heavy diet. As soon as I cooked the first meal for him - Puerto Rican style rice and beans - he changed his tune. When I gave him some peanut carrot soup, he was singing. :) His idea of "healthy" is salad, and conversely, my idea of "healthy" is preparing almost any dish in a conscious way.

You need to really decide if this is a deal-breaker for you. I think that it's easy for him to adapt to some of your healthy habits if you're grocery shopping and cooking, for example, but it's not a guarantee.