I have committed adultery many times during the past 30 years of my marriage and in many instances lied to cover up my absence. During the last year or two, I have earnestly started to read the bible and now feel extremely guilty about my past poor behaviors. Since I have become more familiar with the bible, I see many things differently and have completely changed the way I am living my life. I have started to attend church regularly and I am starting to get settled with a good bible study group. I know that I have broken many commandments in the process of committing adultery and the process of living my life. I have asked God to forgive me. I am trying to be a good husband to my wife and have always loved her despite the years that I made many bad decisions. I am truly sorry for all of this now.
The good news is we are still married and are completely happy for once in our lives. My problem is now, how do I repent for all my past poor behaviors? I know that she will divorce me if I tell her of my past. Is it possible to earnestly repent to God alone for my past sins of adultery and ask for his forgiveness without having to put my wife through this pain? Her health is not good and I am afraid that this would only make it worst. This obviously would devastate her and under the circumstances, I know that she would ask for a divorce. I know that my past is in the past and I have turned from my ways and desire to commit myself to Christ for the rest of my life. Your insight into this and suggestions would be greatly appreciated.
Repentance means changing your mind about sin and changing your behavior (See: Repentance). You are doing this. A part of that change is correcting past wrongs, and again you are doing this. You are now the husband you should have been. It is a mistake to assume that telling people all the wrong you did is fixing your wrongs. It might be a necessary step to get problems solved in some cases, but it isn't the solution.
Bringing up your past isn't going to help you or your wife. "Brethren, I do not count myself to have apprehended; but one thing I do, forgetting those things which are behind and reaching forward to those things which are ahead, I press toward the goal for the prize of the upward call of God in Christ Jesus" (Philippians 3:13-14). Don't ever lie about who you once were, but when a person makes a radical change few people are interested in the past. I would think your wife is so happy about the man you've become that she won't want to ask about the man you used to be. If the topic ever comes up, simply ask why she wants to know about things that you now regret ever doing. If you get a good answer, then tell her only in generalities that you've sinned and thankfully learned before it was too late that you had to change. The main thing is to make sure it is clear there is now a difference between the new you and the old you. "What fruit did you have then in the things of which you are now ashamed? For the end of those things is death. But now having been set free from sin, and having become slaves of God, you have your fruit to holiness, and the end, everlasting life" (Romans 6:21-22).
The times when confession is needed is when the other person is harmed by not knowing or when they do know and they need to know that you have changed so that they can forgive. This is why we confess our faults to God -- He already knows and our sins harmed our relationship with Him.