My prayer for you and your wife is that this has all been a misunderstanding. Since he was a friend of the family, for all we know she could had been giving him some counseling or praying for him as a sisterly brotherly relationship.
Heavenly Father I pray the truth does come out and that this woman has not been unfaithful to her husband at all, but that she was just being kind to a friend of both her husband's and hers. May they be able to walk forward with forgiveness and trust in their heart. May they be as forgiving as you are to us even while we are still sinners.
Give them your peace and wisdom to work at their marriage without accusations, misunderstanding, infidelity, and allow you to work in them and their marriage. I ask this of you in Jesus name, amen.