Find out why your friend broke up with a girl. It will be key for further conversation. Politely ask the guy to tell in detail what happened, how long and why.
Try to convince the other that the cause of the breakup was really serious, and the other way just could not be. Tell him that, of course, he's right in this situation and acted like a real man, not allowing myself and my girlfriend suffer from unnecessary relations.
Ask, did the guy to my former deep emotion. If the answer is you will only have again to praise him for what did not endure, and immediately left the girl "heart is not in it". If your friend responded positively, convince him that the feeling was fleeting, and soon he completely forgets about it.
Discuss the girl that was terminated relationship. Find out what she had flaws, but do it as gently as possible so as not to offend the guy even more. Tell me, what he did was right, stopping to meet a girl that is not worthy of him.
Tell a friend that there are many good girls, and such a confident guy like him will find a new object for the relations. Tell us what other strengths are the guy to give him more confidence.
Involve your friend in some interesting activity that will help him to forget about personal problems. It better be purely male, for example, go together fishing or even hunting, sports match, supporting our favorite team. And, of course, sport is one of the best cures of depression: sign up with another gym and dedicate some time to persistent training.
Try to help a friend in search of a new girl, if he wants to start a new relationship. If you are familiar with lonely and interesting girl, try to organize their meeting or visit one of entertainment and help the boy to meet someone new.