First of all, you need to recognize that whatever happened, you were both at fault, now, if you cheated, maybe was because he wasn’t giving you what you needed so you looked elsewhere, but if he cheated, you were the one who was not giving what he needed, the cheater is morally culpable for the cheating, the moral responsibility does not lie with the person who was cheated upon, but the fault lies in both party’s laps.
It is important to forgive and forget, true forgiveness means that you let go of all of the anger related to the incident, you should never bring it up again, and you should never let it cloud your relationship, if you cannot do this, you will not get guy back any time soon, if you were the person at fault, apologize and mean it, when you say you are sorry, you have to commit to changing, otherwise, if you don’t mean it, you probably won’t get guy back.
Be prepared to chase him a little, this doesn’t mean sending him hundreds of text messages or stalking him, but you have got to show him that you are still interested in him if you want to get guy back, you can’t expect him to come running back just because you have sent out some modest signals that you are ready to restart the relationship, put your ego in check and put your heart on the line.
You might have to settle for something less than you wanted, it might be that he is only ready to be friends when you want a fully fledged boyfriend, it might take time to rebuild the trust, if this is the case, you need to give him the space he needs to get to know you once again, accept that you have to take what he is offering right now if you want to eventually get back with him.
Finally, you have to know when to give up on the get guy back strategy, sometimes you just have to move on, if your boyfriend is unable to forgive you, you are in a position where the best thing you can do is move on and enter into new relationships, while this will break your heart right now, who knows, it might be the best thing that could have happened to you.