Disable textboxes if Combobox is not selected first

Hello, i have a userform with combobox and textboxes and commandbuttons.

I just want to disable the textboxes if user didn't pick a month.

Example: If user try to enter a data in a textboxes without picking a month first, a message will prompt "Please Select a month".

I have a code for this, but when i select the commandbutton or exit the userform without selecting a date, it still prompting the message. I want this for textboxes only.

Private Sub ComboBox1_Exit(ByVal Cancel As MSForms.ReturnBoolean)
    If Me.ComboBox1.ListIndex = -1 Then
        MsgBox "Please select a month", vbExclamation + vbCritical, "Error"
        Cancel = True
        Exit Sub
    End If
End Sub