River really, truly scared him when she told him, with with no restraint, just how dark the path he was headed down was - so much that he attempts to entirely change the course of his life by letting the universe think he’s dead and eventually erasing his name from their records when that turned out not to be enough.
But he can’t just stop being the Doctor with everything that name means just by letting the universe think he’s dead. When he thinks he’s won and gotten it all figured out, he is so happy. He’s going to go have adventures, fill River’s nights, and put being the Doctor as a frightening legend behind him (he wasn’t even initially planning to tell Amy and Rory that he wasn’t dead), but when he’s in the Dalek Asylum and Oswin says to him that the Daleks grow stronger in fear of him, it crushes him as she says, word for word, what River said the day he knew for sure he had to do something about himself (the day he failed the people who mattered most to him). It’s harder than he thought to stop.
He is still on that dark path he wishes he wasn’t on. He is always the Doctor - the legend, the hero, the villain - but he continues trying not to be someone the universe fears. He starts erasing the records of the things he’s done, creating a world where River gets pardoned and is free because the man she killed doesn’t exist - a world where River’s name won’t scare the Daleks anymore simply for having murdered their seemingly indestructible enemy. He wants to live in a world where his name alone isn’t so big that people act in fear of him.