The Women - 4:129
You cannot treat women equally, no matter how much you want to. So do not incline wholly to one and leave the other in suspense. If you correct this situation and become virtuous, Allah is Forgiving, Merciful.
When polygamy?
The Women/4:3
If you fear that you cannot do justice to the orphans, you may marry two, three, or four wives as you see fit. If you fear that you cannot treat them equally, then limit yourself to one, or to those to whom your oaths/agreements entitle you. This is the best for you not to deviate