I want to lose 100lbs

Sinice I was in high school I have been over 200lbs and now I am afraid I am close to the 300 lb mark. I do not want to be this big. I would love to be under 200lbs before my 5 year anniversary. I was so over wieght at my wedding that I wont even show the pics and I would love to have a renewal wedding with pictures that I can show to friends and family. I have two years and I want to do it the right way so it stays off! What motivates you and how much do you want to lose?