Two things - when you use combos to filter results, you usually don't bind them to a field because choosing a value saves that value in the field. So the fix is to remove any control source property for the combo. You then need a macro or code to filter your form based on that choice (typically the control AfterUpdate event).
The other thing is, there is no such thing as closing Access and expecting you can control what has been saved or not. Access is not like Word or Excel. You change data in any bound control or query field and the change is done - immediately at the point that you do anything to save the record. This includes, but is not limited to, moving off a record, moving from a main form to a sub form, or running any code or macro that causes it. Don't think that because you close the db without clicking the save button that you can undo any changes. You might want to research some term(s) like "ms access use combo box to filter records" or some such thing.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.