feeling super guilty about eating?

Okay so I have never been slinny my whole life, currently I am 5'9 1/2 and a size 10-ish, and 173 pounds. I hate my body so much. So basically I decided to start the slimfast diet a week ago (been on it for 6 days. Basically you eat two meal replacement shakes, three 100 cal snacks, and one 500 calorie meal. Yesterday I cheated and I ate something from a school bake sale, and I had way too many snacks, I probably had 2000 calories. I used to eat like that all the time, but why am I feeling so guilty about eating more than 1200 calories or less a day? I was put on anti depressants on January 11th after a stay at the hospital for suicidal ideation. My best friend is struggling with anorexia currently, and I really don't want to fall down that hole. Today I drank one shake (I use 30 cal almond milk) so about 150 calories and two 90 calorie fibre one bars. I already feel so guilty and I don't know what to do:(