Why does Dido refuse to look at Aeneas in Aeneid 6.450–476?

This passage takes place in the Underworld, and is a confrontation between the ghost of Dido and the living Aeneas, who has been allowed to visit the Underworld so that he can speak with the ghost of his father. It follows on from the events of Book 4, during which Aeneas was a guest in Dido's home. In Book 4, Dido and Aeneas had been in an unofficial relationship, with Dido especially head-over-heels in love with Aeneas, and Aeneas also very much acting as if he were in love with her. Although we are not told explicitly whether he truly loves her or is pretending (in order to ensure that she will continue to be a good hostess to him and his men), we know that Dido believes their relationship is a true marriage. Aeneas is told by the gods that he must leave Dido's home in Carthage and continue to Italy in order to fulfil his destiny of founding Rome. He decides, instead of telling Dido the truth, to act in (what has been seen as) a cowardly manner and tries to leave without telling her. However, she finds out, and they argue over what is essentially a technicality: she claims that they are married, and therefore he must stay with her, whereas he claims they were never truly married. She explicitly tells him that if he leaves, she will die, and this comes true: as he is leaving with his ships, she builds her own pyre and commits suicide. This means that when he claims in Book 6 'nec credere quivi hunc tantum tibi me discessu ferre dolorem' ("and I did not believe that my leaving would bring you so much pain"), neither Dido nor the reader can believe him; she had made it very clear that his leaving would bring her unimaginable pain, and that she would die. His prior deceptive and manipulative behaviour towards her makes it impossible for her to believe his empty words now. Even the tears he sheds when he sees her ghost ('demisit lacrimas' "he poured tears") can be interpreted as tears of personal guilt rather than true sorrow, and therefore do not persuade her. It is no surprise, then, that she is described as standing "as though she were made of hard flint" ('quam si dura silex') and refusing to look at him.