Sense and Sensibility Chapter 15
During a visit to Lady Middleton's the next day, Marianne creates an excuse so she can stay at home. Mrs. Dashwood expects Willoughby will visit while they are out, and this is fine with her. They return to see Marianne crying, and running up the stairs. Willoughby is downstairs, and admits it is he who caused her sadness, because he has to leave Devonshire, and does not expect to be back for many months. Though Mrs. Dashwood invites him to visit their cottage, he denies this possibility, and leaves in a hurry.
All are concerned at this sudden change in Willoughby's behavior, and guess at the cause of his leaving. Mrs. Dashwood believes that Mrs. Smith learned about Willoughby's regard for Marianne, and not approving, sent him away. She believes Willoughby is engaged to Marianne, but unsure of how to tell his benefactress; he has instead followed her orders to leave. Elinor accepts this scenario, but with some suspicion at behavior so out of character. Elinor does not doubt their affection for each other, but she does doubt their engagement, and that is what makes her nervous. Her mother is convinced both of the engagement and of Willoughby's good character, and she scolds Elinor for her suspicion.
When Marianne comes down for dinner, it is clear she has been crying. Just the mention of Willoughby's name sends her into tears.