You can understand the confusion and resentment of a young man, caused by wounded pride. But you better banish those emotions. Calm, discretion, common sense is what you need to build, if you've decided to return the favorite.
In any case, do not make violent scenes, reproaches, especially with threats. And, of course, don't even think about having to return to your favorite strength. First, no wonder folk wisdom says: "love can not be". Secondly, we are still talking about a civilized man, not the savage.
It should also "take down", telling a girl how you feel without her, how you feel bad. The result is likely to be directly the opposite of what you expect. Can a girl feel sorry for you, but not love.
Wait some time, it is necessary to lay down strong emotions. And then take care to remember and consider: what led to this outcome? It is not just, not on a level the place your girlfriend suddenly stopped loving you. Had to be a reason, and serious. It's not easy, because men and women have different psychology, views on one and the same. If you do find it difficult – ask for advice from your friends, relatives.
If you understand the reason for the breakup and make all the necessary conclusions, your problem is already half solved.
In advance tune in to what you will have to show patience, and tact. Let them know the girl: despite your separation, you still like her (the word "love" yet to say it is not necessary), ready to be her friend, help and advice when needed.
Unobtrusively, tactfully start a conversation with her, ask her things, progress, offer help. Your task is to ensure that the girl herself accustomed to the idea: let the former relationship no, but I still care about you can rely on him.
As soon as you feel that she "melted", and no longer feel any resentment toward you, try to openly explain. Assure that a lot of thought about what happened and are ready to behave differently. Ask her to explain what her you didn't like what you've done wrong? And further already all depends on you.