The kiss between Rhet and Scarlette on the bridge as he leaves her on her journey home to Tara is the most romantic kiss ever filmed
VERY intriguing part of the story indeed! I interpret the scene as Rhett sort of wanting to impress Scarlett and also Rhett wanting to experience the Battlefield (I still giggle when I think of his reasoning for staying in Atlanta was because he's never been in a siege before and wanted to experience it firsthand).
I also think his Leo Moon is coming in. Sure he may be a scoundrel and all but he still has a strong code of honor within him no matter how much he despised Southern Conventions and how criminal he could get and I always believed there was a deep part of him that still seek to respect the South no matter how much he despised the customs as seen during Bonnie's years in the story and later when he tells Scarlett he might end up going back to Charleston to make peace with his people.
Yes I am especially touched when he told Scarlett that he's already getting old and at his age is the time when a person starts realizing traditiona nd starts to reflect on and respect it. As he stated an age when a man realizes all the years gone by.
So I think its a matter of Honor why he went to fight in the final year of the doomed war.