What is the ruling on my actions and my supplication for my husband's death during the last ten days of Ramadan, due to my feelings of disappointment and injustice because he did not fulfill his promises and allowed his mother to insult me, and what is the way to minimize the harm of my supplication?

The Prophet, peace and blessings be upon him, forbade supplicating against oneself, one's children, or one's wealth. He also forbade transgressing in supplication, such as a person supplicating against their oppressor with something that exceeds their transgression. You have done well by repenting. Know that a supplication that involves sin or severing ties of kinship is not answered. Likewise, a supplication against oneself or one's child made in anger is usually not answered. This is due to Allah's forbearance and kindness towards His servants. The foundation of the relationship between spouses is affection, mercy, and overlooking faults.