Why did you choose that ending for Dear John (John and Savannah not being together)?

Because that bittersweet ending, to me, generated more authentic emotional power than either a tragic or happy ending. Moreover, it seemed to fit the story. Keep in mind that I write "modern-day Greek Tragedies" which necessitate an ending that, generally, is either bittersweet or tragic. I try to vary the endings in general so the reader never knows what to expect. Surprise is the final element of the modern love story.