Does she even notice you're not around anymore? It probably doesn't seem like it since she doesn't call or see you much. But inside her mind I can tell you that she still thinks about you. It is virtually impossible to completely forget about someone you have been in a relationship with for so long. The first time she goes to places you used to visit together her mind will drift back to those times. Same thing for the other hundreds of activities you did with her in the past.
But how can you get her to miss you like crazy? The simple answer is by disappearing from her life and creating curiosity about what you are up to. This isn't necessarily the easiest plan to pull off, but it is very effective for changing her feelings about breaking up with you.
The first thing you need to do is get out of the house and go make a name for yourself. Reconnect with old friends, get more involved in your social circles, and start creating your own fun. Don't wait to be invited to a party or event...come up with your own ideas and invite the people you know. Take advantage of every opportunity to be seen. Helping friends with their own projects is a great place to begin if you need ideas.
Now, while you are out having fun you want to make sure your ex girlfriend sees or hears about your activities. Facebook is one way to do this. Even if she has dropped you from her "friends" you can still find your way onto her page by appearing in other friends pictures and conversations. Remember that the more activities you participate in the better your chances are to show up on her radar.
If you do all this right you will build up a rock-star persona that will make your ex girlfriend think she was crazy for letting you go. The key for you is to play "hard to get" for a while and make her miss you to the point that she will ask you out!
You might have your doubts as to how effective this plan can be. Most people never put in enough effort for it to impact their ex's feelings. It is an all-or-nothing type strategy. Unless you achieve the highest levels of social prowess within the common friends you and your ex have then the results will be less effective. But those who do establish a high level of popularity will discover a whole new world of opportunity. Perhaps even enough to leave their ex behind.