The paired butterflies are already yellow with August (23)
This image reminds the wife of the absence of her lover. The pairing of the two butterflies is like the bond of marriage between the merchant and the speaker, which is why the sight of them causes her pain.
And I will come to meet youAs far as Cho-fu-Sa. (29-30)
The isolation has made the wife willing to travel what must have been weeks in order to see her husband once again, which shouldn't surprise us now that we know her lonely and isolated history.