First of all, stop knocking yourself for being human.
Everyone has slipped up on their journey, some of us a few times more than we'd like to, but we always get back on track. It's ok to enjoy pizza every now and then, so think of it as one of your "treat" days, and just move on. I love Chinese food myself, and we go to a buffet once every month or 6 weeks. I let myself enjoy it- but I make sure I grab high protein and veggie stuff first, with a little couple of treats on the side.
If you love pizza, but have a hard time giving it up, how about allowing yourself a couple of slices once a week, so long as it is within your calorie range for the day? Just eat low calorie veggies and fruit that day, and enjoy the pizza for your dinner with a side salad or more veggies.
My oldest daughter is 16 and is dieting (she has 20 pounds to lose), and pizza is a staple in her diet. She sometimes eats it twice a day, but counts the calories of each slice and stays within her calorie limit. The rest of the day, she has a high fiber cereal, fruits, and veggies. Pizza is not off limits, so long as you count the calories.
However, if it is a trigger food for you, you may need to limit it as to how much you have it while losing weight, hence why I said above, have it once a week or every other week.
As one great poster once said here (kaplods) "this isn't a race to the finish line."
Hang in there, keep posting, and don't let yourself get discouraged. You CAN do this!!!!