Hey there DeathArrow,
Whew have I ever been there! Once upon a time I used to weigh myself all the time. Each time I gained a lb or 2 even though I thought I was "good" I'd just lose it and figure what the heck, I might as well eat a whole pizza and top it off with a pint of ice cream - and that was breakfast.
Now, I know I'll slip-up from time to time. I try to avoid situations like street festivals, super bowl parties, or birthday celebrations where I might be tempt to indulge in "forbidden" foods, but I refuse to skip all the fun activities with family and friends just to avoid temptation. I also threw out my scale (by the way) because it was causing far more heart ache when I failed, than celebration when I was successful, and used how my clothes were fitting.
But mostly I learned not only to forgive myself for being human, but to actually kind of celebrate my indulgence (hey, hey I got away with something). I take the opportunity to really look at which "bad" foods I really enjoyed and which I ate for reasons that have nothing to do with taste, but maybe from habit... like roasted ears of corn slathered in butter which to me is THE food of a street festival, but not something I really, truely love.
I know the standard issue recommendation is to eat a small meal before going to parties etc. But I have found, much like you did, that it doesn't really work for me, 'cuz I am not eating all that "bad" food because I am hungry, I am eating it 'cuz it looks good. So now I plan an indulgence... will it be a bag of those mini donuts that smell so good, or a piece of birthday cake, or that yuumy spinach dip that may have spinach in it, but little else good for you.
So, at the end of a slip-up day, go to bed knowing that you've had a "free day" and know that tomorrow will be a new day. Don't try to make-up by cutting even more calories the next day, just move on with what you need to do. You have made a decision to lose weight - that is all ahead of you. Keep looking ahead, not back. As the eastern seers say.. you are where your attention is focused. If your attention is focused on the bright future ahead, you will be in bright future. If you are focused on the mistakes of the past, you will be in the past.
Keep up the good work!