If i go back to being vegetarian will i get fat?

Vegetarians and vegans do tend to maintain an healthy weight but if they eat junk food then of course they will put on weight. It does not matter what you eat, if you eat more calories than you burn of in exercise then you put on weight. Vegetarians are generally healthier than meateaters because they are more aware of what they are consuming and take the time to learn about nurition.