Good manners include preventing another person from feeling deliberately excluded. If a confidential matter is genuinely necessary, choose a suitable time and private place rather than creating confusion in a three-person gathering.
Example 1: Two of three friends repeatedly whispering while looking at the third may cause needless hurt.
Example 2: Defer the private conversation or continue a shared discussion until a suitable opportunity arises.
فَلَا يَتَنَاجَى contains a prohibition, while حَتَّى marks a limit or endpoint.