Imagine you are walking a straight and narrow path with cliffs on either side. Wandering off the path will lead to disaster. In the same way, having a wife (or whoever) who challenges foolish behaviour and keeps you from making bad mistakes will keep you out of trouble. You might also hear of a prisoner on release promising to "Go straight" meaning keep out of trouble. This is not quite the same as "straight" as the opposite of "gay" in slang english - meaning heterosexual, but it does have the same sense of sticking to accepted societal norms.

Actually--the correct phrase is "strait and narrow," although the mistaken version "straight and narrow" is probably much more common now. "Strait" is an old-fashioned and out-of-date word that is a synonym for "narrow" (or "tight" or "confined.") It's out of date and survives only in the geographic name, "straits," meaning a narrow passage between two large bodies of water. It's a Bible reference, to Matthew 7:13-14, in the "King James Version," the classic 1611 English translation: "Enter ye in at the strait gate: for wide is the gate, and broad is the way, that leadeth to destruction, and many there be which go in thereat: Because strait is the gate, and narrow is the way, which leadeth unto life, and few there be that find it." To "keep on the strait and narrow" means "take the right path, the morally correct path."

Keeping someone on the straight and narrow is keeping them living a morally correct life. He's saying his wife stopped him from doing the things that men do sometimes without the influence of a good woman (drinking, drugs, bar fights, you know the drill...)

Keeping someone on the straight and narrow is keeping them living a morally correct life. He's saying his wife stopped him from doing the things that men do sometimes without the influence of a good woman (drinking, drugs, bar fights, you know the drill...)

居仁由义