The Prophet PBUH said: "Verily, among the worst of people in the sight of Allah on the Day of Judgment is the man who goes to his wife and she comes to him, and then he spreads her secrets." (Sahih Muslim)
Men and women should both keep whatever happens in their bedroom private, just between themselves. Such matters should not be shared with friends, in gatherings, or in gossip. Doing so is sinful and shows a lack of modesty.
The Messenger of Allah PBUH especially warned men about this, because many men tend to talk about their wivesтАЩ secrets among friends, which goes against decency and modesty. The Prophet PBUH forbade this bad habit so that people stay away from this sin.
The lesson is that whatever happens between husband and wife is a hidden secret. Faith and modesty teach us that this secret should never be revealed to anyone. This protects honor and earns AllahтАЩs pleasure.