The user can still change the value if it's a checkbox, so I don't know why that's a problem, unless the users have to actually see ACTIVE or INACTIVE together to know what's going on.

If that's the case and you really have to use a combobox, then you'll have do something like this:

Make the RowSource array 1 column only
Set combobox.BoundColumn = 1
Blank the combobox.ControlSource.
Assuming that after a record navigation, a form Refresh() is called, in the combobox.Refresh(), put
this.Value = IIF(mytable.lActive, "ACTIVE", "INACTIVE")

In the Valid() or InteractiveChange() of the combobox put
REPLACE mytable.lActive WITH (this.Value = "ACTIVE") IN table