Struggling with Food Restrictions and Body Image

i got super uncomfortable and shit down on the walk back to my dorm because my roommate suggested we go to the donut shop sometime. im already getting food tonight, and i restrict it to once a week because i don't know how many calories are in things. im currently only eating 800 a day, and i know that that is way under what a guy my height should be eating, let alone anybody. but i feel like i need to starve myself if i hit 1000. i dont know how people eat out and stay skinny. i dropped an entire pants size and the new ones are still too loose, and it felt like an accomplishment. i've gotten used to restricting my food and it doesn't bother me until im staring at the cupboard trying to find a snack that i can eat and not feel bad.