It's as they leave Carthage that Aeneas discovers he has begun to forget the beginnings and ends of their conversations--a coincidence so frightful he can only imagine it one last punishment from the gods for Dido's grief. With the years, with the annual smoke and sacraments, he sacrifices one trivial detail after another until he wonders if they might ever have been.
It's in old age that he comes to see this as a gift: in this way, at least, he can learn her anew, can tell himself stories of what might have been and believe them, if only this once.
(A bitter gift on Mother's part; but then again, they always are.)