Paranoia. People in general assume that others think more or less like they do. It would be hard to get over the feeling that others are likely to betray or murder you if it will benefit them, if for most of your life you would have done the same to them.
Of course, this will likely conflict with the character's reformed ideals. So he may instinctively distrust others and be a bit paranoid, but consciously choose not to act on such suspicions.