You are complicating things way too much. Far easier to create a query that references the form combo, base the form on that query which then returns this info to the form. So many ways to do it, but building code for unbound controls doesn't seem to make much sense. The only thing you'd have to worry about is setting the form recordsource after it is opened, otherwise your query may prompt you for the combo value. Or simply load all records (thus query does not use criteria) then filter with the combo. Or don't set the form recordsource until a combo value is chosen. So I'm not saying no code at all, just less than what you describe.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.