Act 2 begins three years later. We see Suzuki praying in front of a Buddha statue. She is praying for Butterfly, who is crying incessantly. When Butterfly hears Suzuki praying, she tells her to stop praying to Japanese gods because they are lazy. The Christian God, she argues, will be much more attentive to Suzuki's prayers, but she worries that the Christian God does not know where they are.
Suzuki informs Butterfly that they are on the verge of financial ruin, nearly out of money. They are dependent on Pinkerton returning and pulling them out of their ruin. While Butterfly is confident that he will come back, Suzuki is less confident, suggesting that foreign husbands never come back for their Japanese wives. Butterfly tells Suzuki that Pinkerton paid the rent and arranged with the consul so that the house would be outfitted with locks, meant to keep out mosquitoes, troubles, and relatives.
Butterfly is indignant when Suzuki tries to tell her that Pinkerton will not return. She insists that Pinkerton promised to come back, but Suzuki feels sure that they are doomed. Suzuki begins to weep. Butterfly sings the opera's most famous aria, "Un bel di vedremo" ("One fine day we shall see"). She dreams of the day that she sees the smoke from Pinkerton's ship on the horizon. In the aria, she sings about how she will wait for him up on the hill, maintaining a demure and coy attitude all the while.
Suzuki leaves after the aria, and Sharpless and Goro come into the house. When Sharpless calls her Madam Butterfly, she corrects him and tells him to call her Madam Pinkerton. She is excited to see him and welcomes him to her "American home." As she offers him an American cigarette, he pulls out a letter he received from Pinkerton that says that Pinkerton is doing well. Overjoyed by the correspondence, Butterfly asks Pinkerton when the robins make their nests in America, explaining that Pinkerton told her he would return when the robin builds its nest. She tells him that the robin has already nested three times in Japan, but maybe it is different in America.
Sharpless tries to cover for Pinkerton, telling Butterfly that he knows nothing about birds. Goro laughs at this, which offends Butterfly. She discreetly complains about Goro to Sharpless, telling him that Goro tried to give her away to a new husband after Pinkerton left. Most recently, Goro wants to give her over to a wealthy Japanese man named Yamadori.
Yamadori arrives at the house, and Butterfly tells him that he ought to give up pursuing her, referencing the fact that he has been married and divorced many times. Sharpless looks at the letter that Pinkerton sent, considers telling Butterfly about its contents, and then decides against it. In an aside, Goro tells Sharpless that Butterfly believes she is still married to Pinkerton, but Butterfly hears him and insists that she is still married to Pinkerton. She tells him that she is an American, and that in America divorce is not so easy, before asking Suzuki to make everyone some tea.
Sharpless and Goro discuss Butterfly's delusions, and Goro tells Sharpless that Pinkerton will be returning soon. To this, Sharpless informs Goro that Pinkerton wants him to try and break the news of the divorce to Butterfly, so that he will not have to confront her himself. He has no intention of seeing her while he is in Japan. Yamadori and Goro leave, as Sharpless sits down with Butterfly and takes out Pinkerton's letter.
When Sharpless reads the letter, which includes instructions for him to prepare Butterfly for the fact that he no longer loves her, Butterfly keeps interrupting, exclaiming her excitement about Pinkerton's return. When he realizes that Butterfly seems almost immune to bad news, Sharpless cannot bear to finish reading the letter. He puts the letter away and asks Butterfly what she would do if Pinkerton were to never return again, which is unthinkable for her.
Butterfly entertains Sharpless' scenario, suggesting that she would go back to singing for money or else, die, if Pinkerton never returned. Seeing an opportunity for the poor girl, Sharpless tries to encourage her to marry Yamadori, but this upsets her and she sends him away. As he goes to leave, she apologizes for being rash and explains that his questions made her feel bad. She then goes and fetches her two-year-old son—Pinkerton's—and brings him to Sharpless. The boy has blonde hair and is a constant reminder to Butterfly of Pinkerton.
Act 2 picks up three years later, when Pinkerton has officially left Butterfly behind. We find Butterfly and Suzuki in their home, on the brink of financial collapse, worrying about what will become of them. While Butterfly is still under Pinkerton's spell, insisting that he will return to them in due time, Suzuki feels equally confident that he has left them definitively, and that he will not be returning any time soon. In this moment, we see that a great deal has changed in Butterfly's circumstances, but her naivety, and her belief that Pinkerton will remain loyal to her, remains the same as it was 3 years prior.
In this Act, we also learn that the couple is officially divorced. When Sharpless and Goro visit Butterfly, they find that she is under the delusion that Pinkerton will be arriving any minute, and that they are still married. Furthermore, even when Goro tries to explain that Pinkerton has divorced her, Butterfly is confident that her husband will come back to her. Here, we see that she suffers from a kind of delusion, a belief in Pinkerton's loyalty in spite of overwhelming evidence to the contrary. Butterfly's defining delicacy is not simply a matter of her beauty and femininity, but also reflective of her mind; she has a delicate response to the tragedies of her own life, choosing what she wants to believe rather than considering the plain facts.
This delusion is upheld by Butterfly's perceptions of her own American-ness, having married an American man. When Suzuki prays to Japanese gods for help, Butterfly derides her religious ideas, suggesting that the Christian God of the West would be far more helpful. In this, we see that her devotion to Pinkerton extends to her sense of Japanese cultural identity more broadly; with Pinkerton, she is not only the wife of an American, she is an American herself. This skewed perception also upholds her delusion that she and Pinkerton are still married. When Goro tries to explain that they are actually divorced under Japanese law, she insists that she is not married under Japanese law, as she is now an American.
Giacomo Puccini, the composer of the opera, pairs Butterfly's more delusional reveries with some of the most beautiful music in the opera, not to mention the operatic repertory more generally. The most famous aria in the opera is "Un bel di vedremo," which Butterfly sings about the imminence of Pinkerton's return. She imagines a beautiful and romantic scene, tracking Pinkerton's imagined return from the image of his ship on the horizon line to the image of him walking up the hill to the house they share. Delusional though she may be, these false impressions provide lush musical and emotional climaxes within the opera.
A tragic element of this act is not only that Butterfly is delusional about Pinkerton's feelings for her, but that Sharpless, when given an opportunity to prepare her for the heartbreak of Pinkerton's abandonment, does not come out and tell her explicitly where Pinkerton stands. His desire not to hurt the poor Butterfly prevents Sharpless from delivering the news that he knows would so devastate her. Yet, it seems clear that Butterfly ought to learn the truth sooner or later, or else suffer an even more devastating loss.