Final answer:
Arthur responds to Guinevere's sin with remorse and seeks forgiveness. Guinevere reassures Arthur that there is nothing to forgive and they are reconciled.
Step-by-step explanation:
In the story, Arthur responds to Guinevere's sin by expressing deep remorse and seeking forgiveness.
When Arthur learns of Guinevere's affair with Lancelot, he is devastated and feels a tremendous sense of guilt. He falls to his knees and pleads for Guinevere's forgiveness, promising to love her and dedicate his life to her.
Guinevere, however, reassures Arthur that there is nothing to forgive and that the only mystery is his love for her. She accepts his apology and they are reconciled.