Originally Posted by RustyCage
I feel his quitting was multi-faceted, personally. It's not just one reason. There's obviously a lot of weight on his mind.
It's not just Rachel, it's not just his not being needed. It's both of those, and more. He became an outcast. He had to have felt horrible about Harvey. The Joker essentially won, and I'm sure that was eating up at him privately.
I always felt the main issue was the Batman wasn't needed anymore, period. But for Bruce Wayne personally? He never moved on with anything in his life because of Rachel and his life was all about an energy project that he mothballed in the end and then went into exile. It only got worse for Bruce Wayne throughout the years after TDK.