Thank you for your letter -- and I too hope your experience will cause someone to think about the broken relationships in their lives and try to do something about them. The Bible says, "If it is possible, as far as it depends on you, live at peace with everyone" (Romans 12:18).
One of life's hardest lessons is that we cannot change the past -- and this is especially true when death intrudes. Then the opportunity to say something we should have said, or to do something we should have done, is gone forever. It is a bitter lesson, and one that leaves guilt and regret in its wake. The only solution is to ask God to open our eyes to things we need to do, and then give us the courage and wisdom to do them.
What should you do? First, seek God's forgiveness for your sins -- not just this one, but all of them. God loves you, and the greatest discovery you will ever make is that He wants you to be His friend forever. By a simple prayer of faith ask Jesus Christ to come into your life. He will forgive your past and give you hope for the future.
Then ask God to help you learn from this experience, and to give you a new love and a new concern for others. Jesus said, "As I have loved you, so you must love one another" (John 13:34).