Why should I follow my diet, if around me everybody looks good and they eat a lot ?

I used to feel the exact same way when I was in high school. It was frustrating to see the skinny girls pig out on junk food while I was starving myself. There are three possibilities why these girls stay skinny...1: they have an eating disorder (they may be purging after eating) 2: they have a really good metabolism (this will catch up to them when they get older, believe me!) 3: they are very active and burn off the calories. Try not to focus on what other people have and just take care of yourself. Eat good, healthy food and allow yourself a treat every now and then. Try to get some exercise every day, even if it's just walking. Good luck!