Cutter, on the first point sure-- call the context or setting or movement from thought to thought casual, and the content philosophical. Both things are true: it is a casual conversation among people who seem accustomed to philosophizing-- in an informal and non-professional or non-academic way-- about matters like the hard work of art, the hard work of beauty, and the conventional denial of those labors. And yes, these are not "everyday folk" in the sense that they seem to be of a class for whom such conversational topics are fairly conventional or habitual or . . . casual. They are comfortable talking about poetry and beauty.

On the second matter, the woman's friend is a bystander in the sense that strong emotion is between the other two, as the final lines make clear. And she is the woman's friend. Specifically, her friend. "Mild" --an adjective that does not suggest even a covert sexual passion to me-- and because "there is many a one who will" etc., in the future, quite possibly younger than the couple.

The silent woman is the love object, in the old high way of love. Her friend is . . . her friend. She is beautiful, and has a nice voice, but the poet's strong, revealed passion, yearning and weariness, aspiration and despair . . . all that is not for her ears. So he says, and the way he says it makes me believe it entirely.

(I don't believe Ms.Gonne is involved here.)