What if you had a peanut allergy, or stomach distress immediately afterwards. Would you really care what anyone thought.
Now if you are sitting at the table debating outloud whether or not you should have something, it would seem that you are encouraging the dialog and what the "okay" to have that which you have your eye on. Yet if you felt terrible later, would your eyes just glance over the item, and move on to more healthy choices.
Sounds like you need to sit down with your BF and have a heart to heart. Why he would discourage something that is a viable option for many, and certainly in the long run only can improve your (and his) overall health is hard to figure out. Yet, this isn't about him, it is your choice, and that needs to be honored. He needs to support you in whatever choice you make. Yet you need to not use him to sabotage your efforts, and then blame him for doing so. I would suggest you just not get into the conversation, and make the decision as to what you will have without his input.
You can also ask the kitchen to make something for you the way you want it made. Many are accomodating. There are also a growing number of restaurants that have separate menus, and that way you can each order what you want, without it being an issue.
I think from your one statement "Wanting to order something I shouldn't" proves that you need to have a conversation with yourself prior to eating out. Look online at a restaurants menu, and decide before you go what you will have. You can also call in advance and ask questions. Just flat out say you have an allergy to these foods. Or perhaps for a few months, you eat in. Learn some incredible dishes that you would much rather eat. You need to have a contract with your self, because the world for the most part does not understand how nutrition plays a HUGE role in mental and physical health.
I apologize if I have come off as too strong on the subject, but I have dealt with many of these issues, and feel very protective of these choices. Plus, nutritional changes are what have returned my daughter's quality of life back to her. Seizure free, med free for seven months.