The Love Interest has noted something odd about their partner. He/she is gone at all hours, does strange things and never answers a straight question. Is he betraying her? Never fear! You Love Interest still has Undying Loyalty toward you and would never do such a thing. No it is something else. Rather he is a great patriot bravely defending his country against The Empire. She of course can't be told about this because she has no Need To Know. So she must wonder. Not necessarily a married couple of course. Subtrope of Mistaken for Cheating. Film
- Pretty much the entire plot of True Lies.
- Not spies, but close enough: Mr. & Mrs. Smith.
- The Incredibles - Mrs. Incredible gets suspicious when she finds a tear in his old costume and what she thinks is Affair Hair on her husband's suit.
- In NCIS, Power Down a young man discovers that his recently murdered wife whom he momentarily thought was cheating was a security agent working to protect The Government against cyberattacks .
- A subplot arc in the first season of Spooks involved the girlfriend of one of the agents adding two and two together to get five. (The time he went undercover as a married man and then forgot to take the ring off before he went home really didn't help.)
Hello, Unknown Troper. You'll need to get known to lend a hand here.