The only thing is to be really, really disciplined with yourself - you have to train yourself to stop thinking about it, as that way madness lies! So, every single time you catch yourself thinking about him or her, make a conscious decision to distract yourself so you think about something else. Treat it seriously, like an addiction or really bad, self-destructive habit that you have to break. I promise, only you will loose if you don't make the active decision to move on. BTW, just like recovering from any other addiction, every day you get stronger!

hmm..that's kind of hard. a lot of questions : does he treat her better?does she make him feel better?does he remember you when they make the same things that he had done with you ..i think it's best to ignore all these questions and start being more interested in your own person.make things that please you :) .enjoy every moment and let your relationship in the past, just like it was.don't try to change anything. so, stop wondering and better smile and show both of them that you're just fine :)

Keep reminding yourself that there was a reason you broke up. Remember all his bad habits - now this new person has to deal with them! This helps take the focus off of the comparison between you and her.