What is the ruling on a man marrying without his wife's knowledge, given that she is fulfilling her duties, and his claim that the reason for his marriage was to escape another woman who proposed marriage to him?

Allah has permitted polygyny for the Muslim man who is able to be just. Polygyny may become obligatory for him when he is able and fears hardship or falling into prohibitions, or to provide chastity for a woman who needs it. It is not a condition for the permissibility of polygyny that the first wife be neglectful, and this is what is indicated by the actions of the Prophet, peace and blessings be upon him, and his companions. We advise the first wife to be patient and seek reward from Allah and not to overstep her bounds, and it is not permissible for her to wish for the divorce of her co-wife or to cause it.