We are all human. We all make mistakes and have done stupid, embarrassing, shameful, and hurtful things in our life. While I have no idea what you did 40 years ago that is still causing you pain, I assume that it is pretty horrendous. My own shameful acts are within my last couple decades. My only advice is to find something that can reverse the harm. Not against the person(s) that you may have harmed (if that was it) since that may cause criminal or civil liabilities or may only open old pain for others, but in a karmic sense. Look for others that you can help and ease their similar pain. Put some good out there to balance the bad that you may have caused. Actually finding and working to do something can give you purpose and motivation. Good luck. Just remember the old saying that we are all villains in someone's story. All you can do is work to be the hero in someone's story.