“I could feel his anguish.” What could be the anguish?

The exact nature of the character's anguish is unknown, as it is up to interpretation. It could be anything from sadness or despair to regret or loss. It could be that the character is feeling the consequences of their past decisions or simply feeling trapped in a difficult situation with no way out. It could be related to a particular crisis in the character's life, or it could be deeply personal and internal. Ultimately, the specifics of the anguish will depend on the context of the story and the character in question.