Breach (2007) on Netflix

In 2001, the FBI clerk Eric O'Neill, who is a specialist in computers but wants to be an agent, is invited by agent Kate Burroughs to work with the senior agent Robert Hanssen, who had worked for many years in the Soviet Union and now is assigned to protect the agency against electronic infiltration. Kate tells to Eric to write down the behavior of Hanssen in notes and send them to her since Hanssen would be a pervert under investigation for his sexual behavior. Eric works with the bitter and rough Hanssen and he finds a family man and devout Catholic who earns his respect instead of a deviant. Further, his investigation and his relationship with Hanssen and his wife Bonnie affects Eric's wife Juliana. Eric tells his opinion to Kate and she decides to tell the truth about Hanssen to him: he is a mole that sold many secrets to the Soviet Union and has compromised the identity of dozens of agents. Eric decides to go on in his assignment despite his friendship with Hanssen and the problems in his marriage.