All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
It is not permissible for a wife to supplicate to Allaah to make her the only wife of her husband who has a second wife, as this is supplicating with a sin. The essence of her supplication is wishing that the bounty (of having a husband) be removed from the second wife. A Muslim woman should not let her jealousy lead her to injustice; rather she should be pleased with the Predestination of Allaah. She should know that this is a trial and she should be patient in order to get a great reward.
The fact that the husband insinuated to her to divorce his first wife is not a sound reason for her to supplicate with the above supplication. Moreover, he is not obliged to fulfil this condition even if you had conditioned it on him before the marriage. For more benefit, please refer to Fataawa 86514 and 91150.
Among the things which help the wife be patient is to abundantly supplicate Allaah to make her patient and she should endeavour to this effect until patience becomes normal for her.
Grieving and being sorrowful is not beneficial, and thinking to commit suicide will not solve the problem; rather if she does so, she subjects herself to the severe threat which is mentioned in religious texts for those who commit suicide.
For more benefit, please refer to Fatwa 84296.
Instead of thinking to commit suicide and the like, the wife has the right to ask for divorce if she is harmed even if she has to pay her husband compensation in return for divorce.
For more benefit, please refer to Fatwa 87728.