A good restaurant rule is: Eat half.
Restaurants have enormous portions, generally speaking, and one of the best ways to reduce your calorie intake (or keep it level) is to cut the meal in half.
Share a plate of food instead of ordering separate meals.
Also, remember that most restaurants have absolutely no problems with you being a little picky.
If you ask for something "without butter or oil" they can usually do that. You can ask for dressing on the side when it comes to salads. You can ask for your chicken to be grilled instead of breaded and fried.
Also, keep your hunger signals in mind. If you aren't hungry when your boyfriend wants something, then let him eat. You can talk and keep him company, you don't need to eat just because he is.
That should be good for a start.
Have fun! Don't focus on the food!