The story ended in book 24, but Book 25, Longfellow's Journal, provides nuanced insight into the character's heart. Line up what he wrote with the events in the Gone series.
Before Longfellow left AromaX, before he realized he was a descendant of TallMan, a wise medicine man who lived in the 1770's, Longfellow opined in a journal, jotting down his secrets, desires, discoveries, and opinions intended only for his eyes... yet now revealed to you in this compilation of his musings.