SW is about living in the real world... it's not a "diet" as such. Special occasions can be worked into the plan. To be honest, it's all the guilt and anxiety that you're already submerging yourself into that sets one up for failure. So forget about it.
Look in the book that you got when you joined SW, there's a restaurants & takeaways section. Check out the syn values to the meals there and choose one to work into the plan. Or go for something that is "dry" like something cooked in the tandoori, as opposed to something oozing in sauce (which is likely to be full of oil, cream, nuts, etc).
Modify your syns either side of the day you're going out for your meal. Remember, you chose this because you want to give your OH a special night out, and he probably deserves it. So relax and enjoy yourself! With just a little bit of forward planning, it doesn't have to wreck your whole week, dieting wise.
I'll let you into a secret, before Christmas, me and one of the women I work with decided to take ourselves out for a Crimbo meal (because our team wasn't going to - scrooges!!) We decided to go out for an indian. I ordered something from the tandoori, which was fabulous and came with vegetables... we shared a naan bread, which I ate a bit of so I felt I'd had a treat... we even had a couple poppadums. I just didn't scoff the whole pot of mango chutney or whatever. But I didn't go without either. I thoroughly enjoyed my indian treat. AND... wait for it... I still had a loss that week.