Pizza! :'(

I woke up this morning and weighed myself.
I had gone down to 50 kg, which I felt totally amazing about. Another kg!
I had a weetabix and some fruit and fiber for breakfast then went to school and didn't eat all day until dinner time (I planed not to have anything for the rest of the day!).
I was out with my friend and her parents and we went for dinner at an italian restaurant so I had to have a whole pizza to myself :S ...It looked about 10 inches, I left most of the crusts and gave a small slice to someone, but it was still pretty bad. I feel so crap about it now, it was covered in cheese. I tried to make myself purge when I got home, but for some reason it didn't work.
I'm really anoyed about this. I was doing so well and now I kinda ruined it..
Oh well..there's always tomorrow. I'm going to starbuks with my best friend for some revision at lunch time so hopefully I will get a drink there and not have anything else for the rest of the day.
I feel exausted but I'm going to do some exercise now to work some of it off.
I'm going to try not to beat myself up too much about this because it was kinda unavoidable. I just have to work extra hard this week!
I've felt so tired since I stoped eating properly, my boyfriend says I've been really emotional and distant with him, so I have to be careful not to let it show too much!