Congratulations on losing 40 pounds !!
What you're experiencing really is perfectly normal. One less than perfect day or weekend of eating WILL NOT make or break your healthy lifestyle. Yes, there are going to be days you eat more than others. Yes, there are going to be days you want to eat more than others and don't care that you're eating too much. As long as don't eat like that every single day, you'll be fine.
There is a notion that once a person loses weight, they can go back to their old habits and eat whatever they want. That is a misconception. In order to take the weight off and keep it off, we must be mindful of what we eat. we must watch our portion sizes and we must get some regular exercise. However, that doesn't mean we can't have some fun once in a while.
You're a human being, not a machine. You don't have to be perfect to be healthy. But once again, as long as this doesn't happen every single day or weekend, you really will be okay.
It's when those bad habits start creeping back in that the weight starts creeping back up.
Moderation, not deprivation.