What happened to get you to this point where you need to know how to get an ex boyfriend back in the first place? You need to take an honest look at what happened in the relationship. Was it something that you did or something that he did? If it was something that he did, you may want to rethink the whole thing because you need to be absolutely sure that he isn't going to do it again. If it was something that you did then what was it that brought you to the point that a split would happen? What and where did things go wrong? Most importantly, what is going to keep it from happening again? You have to have an answer for this.
What is going to be done differently if you are successful in finding out how to get an ex boyfriend back? Why should he believe that things are changed or will be different? Are you changing some things? Is he? This will take more than just words and a desire to be better: it will take action. It will take effort on both your part and his. In this you must be willing to lead by example and you may have to prove that you are trustworthy in this before he will give you another chance.
Proving to him that you are able to have a better relationship may be the most difficult part of it. If there are mistakes that have been made in the past that kept recurring, how can you prove that it won't happen again? Only one way it can happen and that is to be incredibly diligent in your efforts to not let that happen again. If someone wants you to stop smoking and it is important to not let them down then how are you going to show that you can stop? Easy answer, you don't do it anymore. You avoid situations where you are likely to crave it or where you might be tempted to do it. You also seek help. That is what it is going to take with learning how to get an ex boyfriend back.
You won't be able to do it on your own. Restoring a broken relationship will take more than your efforts and desires. It will take both of you. You need an ally to help you get things back together. Once you have gotten your ex boyfriend convinced that it is worth working on then you will have your ally and will have found out how to get an ex boyfriend back.