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.
It is forbidden for a woman to stipulate that her husband divorces her co-wife. It is reported in Saheeh Al-Bukhari and Saheeh Muslim that the Prophet said: “A man must not make proposal of marriage to a woman when his brother has done so already. And he must not offer a price for a thing for which his brother had already offered a price; and a woman must not ask to have her sister divorced in order to deprive her of what belongs to her, but she must marry, because she will have what Allah has decreed for her.”
This Hadeeth limits the general meanings of the Hadeeth in which the Prophet said: “From among all the conditions which you have to fulfill, the conditions which legalize for you to have sexual relations (i.e. the marriage contract) have the greatest right to be fulfilled.”
Therefore, what you and your husband had agreed upon is forbidden and what is forbidden should not be implemented. All these given details are in regard of fulfilling the conditions.
Now, we advise our questioning sister to abstain from asking divorce as long as your husband is righteous, as you mentioned, and did not violate your rights. Know that you did not like to be divorced, likewise, you should not like for anyone to be divorced. The Prophet said: “None of you truly believes until he loves for his fellow brother that which he loves for himself.” [Al-Bukhari and Muslim]
Know that polygamy is permitted in Islam and it was the practice of the Prophets.
Also, we advise the husband to turn towards Allah in repentance for his lies. He should try his best to please his wife and be good with her.
For more benefit on polygamy, please refer to Fataawa 82971 and 81469.
Allah knows best.