Why do you mention weakness? You can't blame anyone for "an affair" when you don't know the nature of the relationship with their spouse and the private agreement they may have.

Some people don't believe in exclusivity or monogamy, some people believe in a clear separation between love and sex, some marriages/partnership are over for years but partners have a tacit agreement to pretend for various reasons instead of divorcing, etc.

Are you privy of their life?

Affairs could be leverage for blackmail. Affairs with subordinates carry the risk of sexually harassment lawsuits. Affairs with conflicting interests or foreign nationals have more implications.

He apologized to his family, therefore one would assume they weren't aware of it.

Edited my post for clarity. From the board's point of view.