He didn't really betray her.
She was always far more into him than he was into her, because Venus (Aphrodite) asked Cupid to take the guise of Aeneas' son and basically form an attachment between them, you will remember. So when they spent the night in that cave, she thought they were married, while he never really took it as seriously.
Later, when Jupiter (Zeus) sends down Mercury (Hermes) to tell Aeneas to go away and keep searching for his new land, Aeneas plans to leave without telling her (try searching for 'stoicism', and you will understand what was going through his head). She is understandably upset about this. They fight, he tells her they were never married, and he leaves.
She feels betrayed because she feels he is walking out on their marriage, their love.
Aeneas last sees Dido in the Underworld. Aeneas and the Sibyll goes to the Underworld to see Anchises. Dido lives in the Underworld with her husband Sychaeus. Aeneas tries to talk to her, but she does not look at him.
The final song at the end of "Dido and Aeneas" is known as "Dido's Lament" or "When I am Laid in Earth." It is a powerful aria sung by Dido as she prepares for her death, expressing her sorrow and lament at being abandoned by Aeneas.
dido
Dido
When Aeneas leaves Dido(Elissa)(Arsilla) She comitts suicide by stabbing herself.
Venus makes Aeneas fall in love with Dido. She sends her son Cupid to take the shape of Ascanius. While on Dido's lap, Cupid makes Dido fall in love with Aeneas. Later on, Jupiter sends Mercury to visit Aeneas and tells him that he must move on to Italy.
'Dido's Lament' in Dido and Aeneas by Henry Purcell
Dido of Carthage
The three wives of Aeneas were Creusa, Lavinia and Dido.
In Carthage.
opera
Dido was abandoned by Aeneas, as Mercury told Aeneas that he must travel to Italy and leave Dido, as Mercury reminds Aeneas that Dido is not part of his fate. Dido proceeds to kill herself out of sorrow by stabbing herself with an "ensis" (sword).