Delete selected item in listbox c#

I KNOW there are ways to remove item from database and my question is because the data is stored on BOTH the database and listbox, how am I able to do so? As in, when the user adds an item, it gets listed in the listbox and then has the choice to remove the item [which is done by selecting the item in the listbox and pressing the 'remove' button.

To remove the item from the listbox, I have a current function that does it. But Im wondering how I can remove from the database also, because to remove it from the database, I need to first select it in the table be it by its id, or name or something. However, because the item is added into a list and retrieved by my 'remove' button as a .Text, then how do I get the [eg. id] of the selected item to be passed into the SQL query to be deleted?

My currently remove button codes is this.

protected void removepromo_Click[object sender, EventArgs e]
{
if [ListBox1.SelectedItem.Text == null]
{
promovali.Text = "Please select an item for deletion.";
}
else
{
string remove = ListBox1.SelectedItem.Text;
ListBox1.Items.Remove[remove];
}
}

As you can see how the item is removed from the listbox, my question was how do I make the system retrieve the id or name of the 'remove' string and pass it into my SQL query for deletion?