Relationship and infidelity do not go hand in hand unless you are madly in love or you have no choice other then acceptance. In both the cases of acceptance one need to maintain the emotional thunder within.
To make a relationship work after such a roller coaster the foremost thing we need to do is not to "SHOW" it to the partner that you are trying to do thing only to save the relation. Doing this hurts the partner and adds to the guilt of cheating that might be already killing them. Some might also think that you are trying to gain an upper hand in the relationship because of the mistake made by the other one (this is practical and true).
To further smoothen the things in the relationship understand the reason of your partner cheating on you and never try to adopt the things the other X person had so that you can attract your partner. This only flashes back your partner to the so called mistake made.
Try all the goods things you can think of with your partner and be yourself. Accept the fact that loosing the path is a innate nature of human and proceed with a good spirit. This helps both rejuvenating and adding emotional dependency to both the partners.
The key is to forget and follow your mind and sometimes your heart too in breaking free and following unconventional ways of forgiveness because after cheating your partner would have never came back to you if they were not yours.
So respect the face that they are still with you despite all the odds and love each moment of it to the core.
It is very rightly said "Love sought is good but given unsought is better".
Take that little extra effort give that little unsought love and you can make anyone yours.