In Death of a Salesman, why does Willy remember being caught with a woman in a hotel room in Boston?
It was Biff who inadvertently caught his father with the woman in the hotel room. Biff had gone to seek his father's help in getting a failing grade reversed. As usual, Biff depended upon his father to get him out of a bad situation. When Biff walked in, his relationship with his father was secure. By the time Biff ran out of the room weeping, the relationship between Willy and his son had been destroyed, setting up the toxic nature of their adult relationship.
Willy tried hard to keep Biff from realizing why the woman was in his room, but he failed. Then Willy tried to control Biff's reaction to the truth, without success. Biff's tears began as he said, "You--you gave her Mama's stockings!" Willy reached for his son, but Biff told his father not to touch him. He called his father a liar and a phony. This experience lay unacknowledged between Biff and his father thereafter.
At the play's conclusion, Willy has struggled hard to hold his life--and his view of himself--together, but both have continued to unravel. His memory of the events that transpired in the Boston hotel room indicate that Willy is reaching the end of his denial. His suicide is imminent.