Why does Alvin Harrison take his own life in the novel, Hope Never Dies: An Obama Biden Mystery?

Alvin Harrison is portrayed as grief-stricken and deeply affected by Finn's death. Later, after Alvin has committed suicide, investigations reveal that Alvin was working with the Drug Enforcement Administration during their investigation into drug trafficking, and had told them about Finn's involvement. His suicide is a response to guilt over having betrayed someone with whom he worked, and with whom he was friends.