Is it permissible for a man to marry a second wife while his first wife is fulfilling her duties, and is the wife entitled to seek divorce because of this marriage, and is that considered an objection to Allah’s decree?

A man's marriage to two, three, or four women is a right established for him by Islamic law, provided there is justice and the ability to manage the affairs of his wives. This right does not change whether the first wife is deficient or not. It is not permissible for a wife to seek divorce merely because her husband married a second wife, as long as he is just and fulfills her rights. If the wife dislikes the legislation of polygyny in principle, then this is an objection to Allah's ruling. However, if she is content with Allah's ruling but finds the matter difficult due to her intense jealousy, then she must strive against her own self.