In Death of a Salesman, why does Miller juxtapose the scene of Linda reassuring Willy that he is a good man with the flashback to the woman?

Certainly there is much irony in this scene as Linda tells
Willy that he is a good man even though he has had an affair with this secret woman. 
Earlier in the play, Linda is seen mending her silk stockings, and Willy feels guilty
because he has bought his mistress several pairs of silk stockings.  Linda is Willy's
strength and the supporter of his dreams.  Although soft-spoken and seemingly passive,
Linda is a strong character who tries to maintain her husband's and sons' visions of the
American Dream.  Willy is not a good man, but Linda reminds the audience that he has the
potential to be.  Willy allows his delusions of himself to overtake his good qualities,
and this scene is representative of that.