Her looks could kill
Mean people suck.

From the film, I always thought he chose to die because she rejected him.
Years later I read the book and it was because he saw in her expression, his death. Not something that would occur to most of us but it was the belief and understanding within his tribe.
I have always depended on the kindness of Strangers - and the bastards let me down!

Jenny was grogeous in Logan Run and America Wolfs movies , hana

I don't think it's years later; maybe about a year. I don't get why the boy commit suicide. We saw this film in my high school senior English class. I was the class film buff and let them know Jenny Agutter was later in Logan's Run and American Werewolf in London.
Mean people suck.

i think his mentioning old Mel getting fired starts her remembering since it was what happened to her dad gone crazy
so A and B, are they so different

One of my all time favorite scenes in Walkabout, her husband is taking and we start to listen to what he is saying then his voice fades beneath the music and the viewer disconnects and becomes part of her day dream. Powerful and well crafted cinema.
I don't think she ever contemplated or regretted not accepting the boy's courtship, that concept was to abstract in the context of the film as they played there roles very alien to each other.
I am sure her comfortable and modern life pales against the rich experience when her life was unpredictable and lost in the Australian landscape and she often recalls these memories as a form of escapism.
Walkabout is rich in "moments" and this would have to be one of the more powerful and poignant sequences.

Definitely B. She was thinking of what could have been and facing regrets for the innocent and carefree life they could have had.

Somewhere between A & B, I think. I also suspect that the point of the scenes with her as a married woman in civilization is that her life is now pretty boring, her husband seems to be a bland corporate tool who calls her "doll." So she fantasizes about her time in the wasteland as Eden.
It's a beautifully haunting scene too, not just in how it's shot but also John Barry's music, one of the few times syrupy strings have actually worked really well as movie music.

If we accept that the reading of The Shropshire Lad over the end scene conveys its meaning then those events never actually happened, at least not exactly as portrayed i.e. nostalgia often distorts memories of the past.