There's nothing wrong with one decadent meal a week honestly. Like I tell my partner - If you don't treat yourself, generally you'll end up 'cheating'. And when you cheat, really the only person you cheat is yourself - cause I mean, they have your money already so you aren't cheating them! I say better to go have a yummy meal that may use some of your weekly flex points than end up sneaking things during the day or night.
Here's what we do, maybe you'll get some ideas
. We go out for a lunch or dinner each week. Lately it's been Olive Garden. We each usually eat 1.5 breadsticks (4 points), he has a salad with 2 tsp of olive oil, I order a soup (Pasta e Fagioli - 5 points per serving, but I usually eat 1/2 serving). When we get our meal we do one of two things. We split a dinner portion and put about 1/3 in the box when they bring it to us and then we both eat 1/3 OR we get a lunch portion, split it in half, and eat the entire thing. There are some really nice low point lunch portions there. Last time we went we got a lunch portion of spaghetti which would have been 7 points but since we split it 3.5 (+4 for the breadsticks and 2.5 for my soup). And it was more than enough food, and absolutely delicious.
It takes a little planning but you really can treat yourself with decadent yummy foods and still stay on plan. You can google the name of the restaurant followed by "weight watchers points" and usually get some results or go to a site like CalorieKing and enter the info in a points calculator. I have a pocket points calculator just in case we go out and I change my mind
Hope to have helped a little!