The best thing to do man is just better yourself and prove her she was wrong about you. Get stronger, get leaner, get faster, get more educated; focus strongly on advancing and starting your career if you're still young. Be the accomplished, wealthy, respectful, in-shape guy and then find another girl. Not only is your ex going to see she was wrong about whatever it is you broke up over, but your also going to feel better knowing you moved on.
When I joined the Marines, I had my ex in mind that entire day. When I finally left for basic, she stopped talking to everyone I associated with. When I graduated from AIT and was shipped out to camp, I made my marine picture my display on myspace and sent her a friend request, and she denied it of course. I talked to her while I was in Afghanistan on IM and she actually had the nerve to say joining the military was dumb of me. The way I see it, I proved her and her mom wrong and they know it.
About a year ago I came back to North Carolina to my hometown (me and my ex lived about 15 miles from each other) and I saw her at a fast food place my wife and I was stopped at. She kept looking at me with her friend. Her friend has 3 kids, all 3 are different races, and all 3 are by different guys. They were looking at us laughing and I was thinking to myself "I save lives everyday, make great money, in great shape, ex-military, I have a family...you on the other hand are 50lbs overweight and haven't had a job in years and let your mother support you and your friends future is on the Maury show taking DNA tests."
I didn't really read the first post, but I hope your ex isn't like mine!