Final answer:
Camilla says she can't marry Richard because it is impossible for them to be together due to societal or personal reasons.
Step-by-step explanation:
Camilla says she can't marry Richard because she believes it is impossible for them to be together due to societal or personal reasons. This can be seen in various examples provided in the text, where different characters express their doubts or concerns about getting married or being in a relationship. For example, in one instance, John feels that he can't marry someone as wealthy as Camilla, while in another instance, Winterbourne doubts that Camilla even wants to marry Richard. These examples illustrate the complexities and uncertainties surrounding marriage and relationships.