How can one deal with the first wife who objects to polygyny, especially since she is a righteous woman and he fears losing her, knowing that the husband wishes to marry to help and repel the temptation of women?

Allah has permitted a man who is able to be just to marry up to four wives. This justice pertains to what is within one's capacity regarding financial support, overnight stays, and housing, not emotional love. Hating Allah's ruling is disbelief (kufr), and alienating people from it is apostasy (riddah). A Muslim woman must not dislike what Allah has legislated; rather, she must believe in it, for polygyny is a solution to the problem of spinsterhood. It is not permissible for a woman to seek divorce without a compelling reason, and if she does, she is sinful. The husband must not build one household at the expense of another and must be just among his wives, for some men may oppress their first wife when marrying a second.