First thing to find out is if the partner was the hunter or the hunted. If they were the hunted then they are much less likely to cheat again once they repent and ask forgiveness. Lesson is to avoid temptation, you know how the prayer goes; "lead us not into temptation". If however, they were the hunter then that can be a much more difficult thing to deal with, where did the temptation arise? At home? a constant feeling? a chance encounter? many questions need to be asked?