Giant containment ward, huh? My guess is that Moldie is stuck there by a ward that Dumbledore created as a last resort, possibly with the assistance of Hogwarts and maybe a few others. The repellent ward was added to ensure that future wizards don't go looking for Riddle and free him.
I think it's cool that he has a girlfriend, but given this type of story, sadly, it won't last.
Hope to see more soon!
Author's response
Shhhh! Your the first one to figure it out. And your pretty much dead on target with your guess. Now lets see if you can figure out what happened to the Wizarding world. All I'm willing to say at this point in time is that I don't think anyone has tried this idea I have. If they have I haven't seen read it.
And yeah your right about the girlfriend as well.
Rob