Can you maybe get them to make up your own version of food there? Such as just some shredded chicken with a tomato based sauce/dressing, some avocado and beans. I know it doesn't sound as great as having the sour cream and cheese included, but if you are serious about being good, you can always ask the question once there.
I agree with driving there, it will force you not to drink as much, one or two won't kill you, if you factor them into your calorie intake (or whichever way you diet).
But I also agree you can't isolate yourself and miss out on seeing friends due to dieting. Not all the time anyway, make this a treat night out and lay low for the next couple of weeks. Also just reiterate to your boyfriend what you are trying to achieve.
SW - 71 kg
CW - 65 kg
GW - 58 kg
Weight Loss so Far = 6kgs
Weight to go = 7kgs