The reason guys often can eat like that and stay slimmer is because of muscle. Have you ever considered weight training? For every pound of muscle you build (takes 4-6 weeks on average), you burn an extra 50 calories at rest. That means, for example, say you lost 5 pounds of fat and gained 5 pounds of muscle (keep in mind although they each weigh the same, one pound of muscle is MUCH smaller and appears smoother under the skin than fat), you would be burning an extra 250 calories a day with no extra effort, weigh the same, but probably drop a jean size or two.
What I'm saying is, the more muscle you build, the more calories you can eat and you will STILL get smaller, not to mention more fit!
Anyway, don't let family or friends de-rail you. I have friends and coworkers asking me why I'm eating so WEIRD when I'm just eating a lot of vegetables. They usually don't have very healthy eating habits themselves and aren't fully comfortable with their bodies, so they aren't comfortable with you making these changes around them. All you really have to say is that you want to eat for health and fitness, and it's a decision you've made that will better your body. I bring my own food to other people's houses and have found ways to be quite polite about it. I simply explain I am working diligently on my fitness, and have a limited amount of calories I can intake. I appreciate the food they are offering, acknowledge how absolutely delicious it looks, but it's important for me to stick to my plan to reach my goals. I have never met anyone who has given me a really hard time, I think it really is about how you approach it. Also, always bringing my own food to friends, work, parties, restaurants sometimes, etc, allows me to control my food and calories while still eating socially!
When you're cooking for your boyfriend, keep in mind all of his lean body mass and THAT is why he can eat those extra calories, his body burns through them. Yours can do the same thing too, but you will have to work for it more because you don't have the testosterone for it
