The most serious breach of trust in Allah’s sight is that a man who has intercourse with his wife, and she with him, spreads her secret. (Using translation from Abū Dāʾūd 4870)
قَالَ رَسُولُ اللهِ ﷺ إِنَّ مِنْ أَعْظَمِ الْأَمَانَةِ عِنْدَ اللهِ يَوْمَ الْقِيَامَةِ الرَّجُلَ يُفْضِي إِلَى امْرَأَتِهِ وَتُفْضِي إِلَيْهِ ثُمَّ يَنْشُرُ سِرَّهَا