Am I sinful for supplicating against my husband with death or that he not marry another woman because of his provoking me with the topic of polygyny, and how can I expiate this sin?

The husband’s method of proposing the second marriage is wrong and provocative, even though the Sharia has permitted polygyny on the condition of justice. The wife does not like sharing her husband, so wisdom and gentleness must be observed when consulting her, and her permission is not a condition for polygyny, but it is preferable. Your supplication for his death is a sin and an transgression in supplication, and you must repent and seek forgiveness from your husband.