Userform: ComboBox Automatically Populating

By changing your code for adding and sorting to this:

With Sheet3
    If UBound(Filter(Application.Transpose(.Range("A1").CurrentRegion.Value), Me.ContextOfUseComboBox.Text, True)) <> 0 Then
        .Range("A1").End(xlDown).Offset(1, 0).Value = Me.ContextOfUseComboBox.Text
        .Range("A1").End(xlDown).Sort Key1:=.Range("A1"), Order1:=xlAscending, Header:=xlNo
    End If
End With