Final answer:
Sophie stayed friends with Agatha in Gavaldon because they shared a bond and supported each other.
Step-by-step explanation:
Sophie stayed friends with Agatha while they lived in Gavaldon because they shared a unique bond and understood each other. They had similar interests and values, and supported each other through difficult times. For example, when Sophie was feeling homesick, Agatha was there to comfort her and make her feel at home. Their friendship was important to both of them, and they found joy and companionship in each other's company.