Great question and answer that explains the need to fully repent of hidden sin not only to God but to those affected even if unknowingly. The question is about adultery but sin is sin. Therefore, I think it has much broader application. A desire to hide a sin of commission or omission from others is a sign of a bad heart attitude toward sin and repentance.
…until you have confessed to him/her and until you have repented to him/her I don’t think you are finished with the process of repenting.
…your sin affects him/her, even if he/she doesn’t know about it.
…be prepared for the consequences of your sin.
…you need to own your sin.
He/She is not to blame for your immorality and your sin, and so don’t imply that he/she is.
Don’t expect that he/she owes you some sort of immediate reconciliation. You are going to have to spend in many ways the rest of your life in your marriage rebuilding the trust that is there, even when he/she does forgive you.
Read the entire post here: http://thegospelcoalition.org/article/does-he-need-to-confess-adultery-to-his-wife