Like Rosamond's father, Lydgate conceals money matters from Rosamond. Moreover, he has begun to realize that his ideal woman is not the best wife for him. He thought he wanted a sheltered ornament. He married such a woman only to discover that he actually needs a partner, because he cannot afford to shelter her figuratively or literally. He feels unable to mention his money troubles to Rosamond. Bearing the burden alone creates an endless cycle of anxiety and misery.
Casaubon pursues a similar path with Dorothea. He treats her like a child because he resolves to "protect" her from Will's supposedly ulterior motives. He convinces himself that Will wants to get Dorothea's money. A woman's safety is a man's concern, not her own.
Dorothea's idealization of self-sacrificing virtue comes to an end. She has tried to submit to Casaubon in accordance with this moral system. However, her idealization of self-sacrifice actually arises from a suppressed pride. She expects appreciation for her submissive self-sacrifice. However, Casaubon considers her self-sacrificing submission part of her duty as a wife, not a mark of extraordinary virtue. He drains Dorothea's vitality and happiness out of her, and she increases his anxieties and self-doubts. The juxtaposed metaphors of youth and death used to describe them come to take on a morbid quality. Casaubon's unnamed promise bears a strong symbolic relationship to the structure of their marriage. Dorothea is never able to agree to his promise. She will never be able to make him happy. His unnamed need haunts her, because she will never be able to please him. The unnamed promise symbolizes the inability of both to fulfill their idealized expectations of one another. It is a promise never spoken, but one that inevitably will be broken.
Once Casaubon cuts him off, Will too must face the need to earn his own living. His driving ambition is social and political reform. He works on Brooke's campaign. His position illustrates the precarious position of the disinherited ambitious young man. He does not have the money to run for election himself, so he must work in someone else's election. His ambitions must be mediated through another, wealthier man.