Dim lll As New ArrayList
 
    Private Sub ListBox1_MouseUp(ByVal sender As Object, ByVal e As _
      System.Windows.Forms.MouseEventArgs) Handles ListBox1.MouseUp
        Dim index As Integer = ListBox1.IndexFromPoint(e.X, e.Y)
 
        If lll.Contains(index) Then
            lll.Remove(index)
        Else
            lll.Add(index)
        End If
 
        Dim LetzterGewählterIndex = lll.Item(lll.Count - 1)
 
        Debug.Print("--")
        Debug.Print(LetzterGewählterIndex)
 
    End Sub