Final answer:
Option 4, 'it would upset our mutual relations altogether,' suggests that Nora fears the impact of her secret on her marriage.
Step-by-step explanation:
The evidence that supports the inference that Nora is afraid of losing her relationship with her husband is found in Option 4: "it would upset our mutual relations altogether." This line indicates Nora's concern that revealing her secret about the money she obtained would fundamentally change the dynamic and happiness of their marriage. Nora's fear is further supported by her actions to keep her financial dealings secret and her reluctance to share the burden with her husband in other parts of the script, reinforcing the idea that she worries about the potential loss of their relationship.