The threads are cylindrical, not tapered, so the cup should feel just about as tight on the first thread as the last. I suspect, that the threads are worn (partly stripped) from riding with a loose cup. I doubt the shell itself stretched since there's just too much meat there.

Without seeing it, I can't advise whether any repair is needed, and if so what approach to take. But it should be repairable at a fairly low cost by a decent mechanic. (finding one is the hardest part). If you'd filled in your profile showing the city, I might have been able to refer you to a decent shop.