What is the ruling of the Sharia concerning a man who remains married to a woman with whom he did not feel at ease after performing the Istikhara prayer before marriage and has not had children with her? Should he divorce her, or should he be patient with her in the hope of having children, while also striving to marry another woman, which has not yet happened?

Your friend made a mistake by marrying a woman with whom he does not feel comfortable. The essence of marriage is stability, understanding, and good selection, which is why the engagement period was legislated for consideration and deliberation. However, since the matter has already occurred, it is advisable for him to be patient with her; perhaps Allah will reconcile them and instill affection in his heart. Allah Almighty says: (And live with them in kindness. For if you dislike them - perhaps you dislike a thing and Allah makes therein much good.) [Quran 4:19]. As for his marriage to another woman, there is no objection to it while retaining the first wife, based on Allah Almighty's saying: (Marry such women as seem good to you, two, or three, or four) [Quran 4:3], provided there is justice between the wives in terms of lodging and sustenance. Justice in love and emotions is not a condition, and the first wife's consent is not required for marrying a second wife unless she stipulated it in the marriage contract.