Relationships are funny things. They make you more frustrated than you have ever been, but at the same time they allow your brain to offer the most sensitive emotions ever. This mix of emotions is good for your body to experience, but not necessarily when you split up. Once you have split up with your partner, all the emotions merge into one, and you'll find yourself constantly repeating the same things over and over again.
Why did they split up with you? Should you wait around incase they change their mind? Do you think they are meeting other males/females as we speak? What are you going to do without them? First of all you need to clear your head of all these negative thoughts. Now I know this is an extremely tough time, but becoming negative and desperate is not going to get your ex back, not a chance. The more negative and desperate that you become, the more likely it is that you won't just lose your ex for good, but it will be hard for others to fall in love with you.
So I guess the solution to this is to stabilize your mind and body. You can do this quite easily by involving yourself with positive friends and activities. This means meeting your happy friends who do things you enjoy, rather than friends that sit around doing nothing all day. Get involved with an old hobby, such as 5-a-side football. Hopefully this will start to clear your head of negative thoughts and give you a better chance of getting your ex back.