Messenger of Allah ﷺ gave us the option (to remain with him or to be divorced) and we selected Allah and His Apostle . So, giving us that option was not regarded as divorce.
خَيَّرَنَا رَسُولُ اللَّهِ ﷺ فَاخْتَرْنَا اللَّهَ وَرَسُولَهُ فَلَمْ يَعُدَّ ذَلِكَ عَلَيْنَا شَيْئًا