Final answer:
The social worker's most appropriate action is to suggest individual therapy to help the husband address his frustration.
Step-by-step explanation:
The social worker's MOST appropriate action is to suggest individual therapy to help the husband address his frustration. While it's important to acknowledge the impact of menopause on desire and provide psychoeducation about it, the husband's belief that his wife may be having an affair indicates underlying trust issues and individual therapy could help him address his frustrations and concerns. Suggesting that the wife have a medical evaluation or offering couples therapy may not directly address the husband's feelings of mistrust and frustration.