Yes, Bruce was under the assumption that once Gotham didn't need Batman that he and Rachel could be together, because she told him that. So Bruce went out looking for someone to take his place so that it could happen. This became his motivation. Then, The Joker just so happen to get in the way of his plan and cleverly twisted Bruce's life. When Bruce was put in a situation where he had to save either Harvey or Rachel, he chose her. When He realized that Harvey was in the room with the bomb, you could tell that Bruce didn't really want to save him, but he wasn't going to just let him die. After Rachel died, he felt responsible for Harvey for two reasons. Harvey was going to take his place to save the city as well as because he knew that Rachel cared for Harvey. Then Harvey died and he felt that he failed Rachel as well as Gotham. In TDKR, Bruce's motive to be Batman once again had changed. Though you could clearly tell he was still in pain after losing her and he still searched for a successor. I agree that the entire film wasn't about getting over Rachel and, just as you said, it was a big part of the film. Rachel, even after her death, was a huge part of the entire trilogy and it wasn't until it was near the end that he finally started to get over her.