Acknowledge your mistake first. Then, try to forgive yourself. Everyone makes mistakes, and this is your chance to learn from it. Focus on doing good deeds in the future.
First, you should realize that what you did was wrong morally. You need to cut off this relationship immediately. Avoid any further contact with this man to prevent more harm to his family and yourself. It's important to respect the institution of marriage.
He might wake up in a completely different world. Maybe technology has advanced beyond his imagination, or society has changed in ways he never expected.