Spend some time alone. Perhaps the desire to return ex-boyfriend caused by the fear of loneliness, habit or the like feelings, and not love. If after a few months or even a year, you'll still feel romantic feelings for the young man from the past, the situation requires an immediate solution.
In order to re-interested in the former man, arrange their lives. It should be rich, interesting and eventful. Sad girl is unlikely to cause a desire to return to her. And here is an interesting young lady with their views and interests will show that it is certainly something you never get bored.
More likely to be ex-boyfriend on the eyes. Surely you still have common friends who will help you meet more often. Their birthdays, weddings and just a party will be an excellent occasion not only to zip past the former, but also to communicate with him. In no case do not mention the desire to return the past at the first meeting. Try to talk to a friendly, learn how he was doing and share their lives.
Try to remind him of pleasant moments connected with you and your past relationships. This can be done in the course of conversation, via the Internet or mutual friends. Think of all the things that he liked and enjoyed. It is these memories in his mind zhivyat your relationship.
Edit. If you broke up, it means that it is in you that is not satisfied. These points have to adjust. Work on a benefit not only to a possible return of the young man, but you most.
Do not return the ex-boyfriend only to avenge him. This will cause him psychological trauma, and you show with the worst hand. Do not despair if you return the young man did not. Life is not so short, and attractive men around enough so as not to suffer for only one of them.