How to get over an addiction?

I have been playing a game called Evony for about a year now. I've known for awhile now that I should quit it, because I became addicted, and it was controlling my life. It's only been a day since I quit and now I feel depressed and have begun to remember things from my past (good memories) that make me even more sad, because I compare then to my current situation. I wanted to know if anyone had any advice for me and how to overcome this addiction.