What is the meaning of the song No Tell Lover?

No Tell Lover is a 1978 song by music group Chicago. What's the meaning of the song and what exactly is a No Tell Lover?

LadyMerton2021-01-17T20:46:39Z

No Tell Lover is one of Chicago’s best known songs, and is about an affair. He loves the woman he’s cheating with more than his girlfriend/wife, but he doesn’t want her to know about it. It hurts him because he knows unless his wife/girlfriend knows about it, he can’t leave her to be with this woman.
https://genius.com/Chicago-no-tell-lover-lyrics