I think they all second-guess themselves, and I think they all experience guilt. I think it was worse for Brem because he was *so* young. He didn't know himself well enough to deal with the repercussions, to move on. He didn't know the universe well enough to evaluate his decision. And he had developed no real ability to trust himself. I think Time Lords are better able to live with the decisions they have to make, because they're used to the idea of having to make them, but I think it's never really easy for them. As I think the Doctor's experience shows. As you say, he is constantly ill at ease with many of his decisions, I think.

Brem made the right choice, and the Doctor usually does, too. But they see all the possibilities of all the timelines not chosen, and I think they're haunted by it.