Unfaithfulness is not a result of a momentary action/decision rather it is the result of a continuous wrong choices.
No one decides in fraction of second to be wrong or to do something wrong. It is always the result of constant thoughts and imagination.
Every wrong actions is made right by justification in passing of time; though the action itself remains wrong forever. The moral degradation can help one to over come the guilt though it is not the right thing to do.
The point of turning back is open, in every moment and time. Provided one is ready to take a decision to be authentic in all what one does.