It's possible to imagine "Adam's Curse" written as a monologue with the poet sitting alone at summer's end. The "beautiful mild woman" would be absent, he would speak her lines, and the woman with whom he as fallen out of love would be in his recollections. That would appear to be the most straightforward way to go about the job.
It would seem odd, though, that his thoughts should shift from the difficulties of poetry to the difficulties of being a woman, and from there, to recall another woman, and then admit to himself he no longer loved her. One advantage of the dialogue form is that it lets the poet assign different parts to different speakers, so that the speeches seem in character. Just as important, love is an emotion between two people, and since lovers' feelings toward each other veer back and forth, the final admission of weariness would not be convincing. When she is present, though, it is convincing and gains additional force from his unwillingness to tell her. John Stuart Mill said that poetry is overheard, and that is what "Adam's Curse" is about.
The conclusion of "Adam's Curse" is masterfully prepared for. Summer being associated with love, summer's end is the appropriate time to admit a falling-out of love. The end of the day is associated with the end of daily labor, which is "Adam's Curse." The pain on the beautiful mild woman's side is brought out by the poet's comment:
There's many a one shall find out all heartache
On finding out that her voice is sweet and low
Immediately after this she points out the labor of being beautiful, as a counterpoint to the labor of poetry. Then the poet complements this on his side with the comment about laborious precedents from old books. The immediately following statement that all the effort of the old love seems now "an idle trade" beings us very close to the conclusion.
But the poet does not place the conclusion at this point: he shows us the evening, and the moon and stars. The six lines beginning "We sat grown" seem to me very interesting. There is a forshadowing of death, the passage to the wholly inanimate world where the people are destined, as the conclusion of weariness. The evening sky is blue-green, which seems an unusual color, but it's appropriate as the color of time's waters. "Trembling" meshes with the rising and falling of time's waters. There is a suggestion that the inanimate world of earth, sky, stars and planets governs everything the three people and everything else in the sublunary world they inhabit.
Reading "Adam's Curse", I thought of all three people as old, even the beautiful mild woman, although there is no actual statement to that effect. It has, I think, something to do with the slow movement of the lines and the length of the speeches.