Regarding the Verse:--"If a woman fears cruelty or desertion on her husband's part." (4.128) It is about a man who has a woman (wife) and he does not like her and wants to divorce her but she says to him, "I make you free as regards myself." So this Verse was revealed in this connection.  

عَنْ عَائِشَةَ ؓ {وَإِنِ امْرَأَةٌ خَافَتْ مِنْ بَعْلِهَا نُشُوزًا أَوْ إِعْرَاضًا} قَالَتِ الرَّجُلُ تَكُونُ عِنْدَهُ الْمَرْأَةُ لَيْسَ بِمُسْتَكْثِرٍ مِنْهَا يُرِيدُ أَنْ يُفَارِقَهَا فَتَقُولُ أَجْعَلُكَ مِنْ شَأْنِي فِي حِلٍّ فَنَزَلَتْ هَذِهِ الآيَةُ فِي ذَلِكَ  

" And if a woman has reason to fear ill-treatment from her husband or that he might turn away from her" (iv. 128) that it was revealed in case of a woman who had long association with a person (as his wife) and now he intends to divorce her and she says: Do not divorce me, but retain me (as wife in your house) and you are permitted to live with another wife. It is in this context that this verse was revealed.  

عَنْ عَائِشَةَ { وَإِنِ امْرَأَةٌ خَافَتْ مِنْ بَعْلِهَا نُشُوزًا أَوْ إِعْرَاضًا} الآيَةَ قَالَتْ أُنْزِلَتْ فِي الْمَرْأَةِ تَكُونُ عِنْدَ الرَّجُلِ فَتَطُولُ صُحْبَتُهَا فَيُرِيدُ طَلاَقَهَا فَتَقُولُ لاَ تُطَلِّقْنِي وَأَمْسِكْنِي وَأَنْتَ فِي حِلٍّ مِنِّي فَنَزَلَتْ هَذِهِ الآيَةُ  

" And if a woman has reason to fear ill-treatment from her husband or that he might turn away from her" that it was revealed in case of a woman who lived with a person and perhaps he does not want to prolong (his relationship with her) whereas she has had sexual relationship with him (and as a result thereof) she got a child from him and she does not like that she should be divorced, so she says to him: I permit you to live with the other wife.  

عَنْ عَائِشَةَ فِي قَوْلِهِ ﷻ { وَإِنِ امْرَأَةٌ خَافَتْ مِنْ بَعْلِهَا نُشُوزًا أَوْ إِعْرَاضًا} قَالَتْ نَزَلَتْ فِي الْمَرْأَةِ تَكُونُ عِنْدَ الرَّجُلِ فَلَعَلَّهُ أَنْ لاَ يَسْتَكْثِرَ مِنْهَا وَتَكُونُ لَهَا صُحْبَةٌ وَوَلَدٌ فَتَكْرَهُ أَنْ يُفَارِقَهَا فَتَقُولُ لَهُ أَنْتَ فِي حِلٍّ مِنْ شَأْنِي