How do I resist eating when my boyfriend eats right next to me? I can't afford to overeat.

Depends. I agree with the other physicians, talking can help. You also need to think about ways to slow down eating. Think of 10 things to do when you feel llike eating, drink water which can fill you up, eat slower and chew more which can fill up your tummy and send signals of being full. If you have a serious weight problem, talk to your doctor about appetite suppressants. And lastly, eat healthy.
Ask for help. Explain to your boyfriend your problem and ask for his help. If he isn't concerned about your health and needs, he may not be the best boyfriend for you. Surrounding yourself with like-minded individuals is key to healthy eating.