You're right: We shouldn't put off apologizing or seeking someone's forgiveness if we need to -- not only because we might not be able to later, but because it's God's will. The psalmist wrote, "I will hasten and not delay to obey your commands" (Psalm 119:60).
After all, think how many years of guilt and conflict you could have avoided if you'd only dealt with this sooner. It probably seemed easier not to confront it and admit what you'd done, but in reality the guilt was always there, and so too was the knowledge that you'd failed to live up to what you know is right. Perhaps your experience will help others overcome their reluctance to face the hurts they have caused. Jesus said, "If you ... remember that your brother has something against you ... go and be reconciled" (Matthew 5:23-24).
It's too late to seek this person's forgiveness -- but it isn't too late to seek God's forgiveness. And you need to do this, because your sin wasn't only against this person but against God. And He wants to forgive and cleanse you -- not only of this sin but of every sin you ever committed.
This is why I urge you to turn to Jesus Christ and open your heart and life to Him. God loves you; He loves you so much that His Son willingly gave His life for you. Don't delay, but give your life to Christ today.