Avi, while you’re correct that not telling her technically will avoid shalom bayis issues in the short term, long term, it’s a recipe for disaster.
Also, a piece of kugel is not the same as another woman.
Also, Goq’s first point about the slippery slope stands.
Kolmevasser drove a chashuv’ah rebbitzen who was decades older. That’s a huge factor. Apparently the rebbitzen a”h had a fine sense of humor.