Hehe, it's harder than you thought, isn't it?
Well don't worry. For my part, the first 2 weeks were the hardest. I agree with whoever said melatonine above, did you know your body produces melatonine after exercise? (Any kind of sports really... ) It's what they call the "hormone of happiness"; not only you get in shape, but you feel great and can sleep like a baby at night. Try to go to the gym, or just go out and walk, run, etc. when you feel like it.
As for the promises, I HOPE you will break them and love someone else, not hang on to her... "forever."
Do something for yourself today :)