Here's an exercise that I decided to try last night and really helped.
Try writing down, in detail, what your future with your ex would be like. Picture yourself in that relationship 6 months in and ask yourself realistically what it would be like on your average days. Focus on the irritations, lack of freedom, pressure and other negatives that were starting to show towards the end...because that's how your relationship would most likely continue.
And, of course, affection and passion always starts to die down long term. So does the laughter and joking. So does the sense of adventure. So do all those deep and meaningful conversations, days and nights out. And don't forget to picture her in her "comfy clothes" without make up, because that's how you'll be seeing her most of your time together. Perhaps you should picture her with a little extra weight and unshaven legs too, because 6 months is plenty of time for her to get complacent about these things...and if you went running back to her after she dumped you, then she knows it doesn't take much effort to keep you.
I was only half way through this exercise and I felt like such relief that our relationship ended. I felt glad to move on without ever hearing from her again.
Another aspect of this exercise is to write how your future would be without your ex and consider all the possibilities and all the freedom you have, how you plan to re-invent or improve yourself, various chicks you could score with, how nice it'll be to date again and experience first kisses, sex and the honeymoon period.
Every time you start to miss your ex, remind yourself what you've written and be grateful for the relationship ending.