All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
The definition of backbiting (Gheebah) is to say something about your Muslim brother (in his absence), that he would hate (to be mentioned), as the Prophet said: "(Backbiting) is saying something about your brother which he would dislike." [Muslim and others]
Al-Haafith ibn Hajar said in Fat'h Al-Baari: "Backbiting is speaking ill of a person behind his back which, if he hears, he would dislike it even if what was said about him was true." [End of quote]
Based on that, if your wife dislikes for you to mention what you said about her to others, then it is considered backbiting, even if your wife will not find out about that in the future.
Allah Knows best.