I am sorry you are hurting so much.

Since the girl you are interested in is currently in a relationship, I suggest moving on. Be optimistic! Believe that the right girl will come along at the right time in your life.

Take care of yourself. Starvation diets or other forms of punishment will not help and are unhealthy and dangerous.

I can understand how difficult it is to make friends... If you consider you have no friends at the moment, take this as a fresh new start. Each day try to take a small step towards meeting new people!

Are you seeing a therapist/psycholosist you can discuss your feelings with?