Originally Posted by Sparrow
Maybe because he thought it would be easier to leave her on the road. There was no telling what she would find at Tara, and if he was with her he might have got embroiled in the situation there.
The way I read it, it was an emotional decision - perhaps actually seeing Atlanta in flames, he could no longer pretend disinterest. But still, I would have expected the immediate needs of Scarlett - and Melanie - to have been a larger influence. Perhaps if she'd been set on self-preservation he would have helped her - but as she insisted on going to Tara, which he told her was crazy, he left her to it.
OTOH, he'd supposedly only stayed on in Atlanta because he'd never been in a siege before, but presumably was really there for Scarlett. If he was braving all that to be around when things kicked off, it still seems odd to me to abandon her for the Cause at the last moment.