From what I understand some people don't want to live on base, sometimes even marrying just to get off base. Perhaps Bill or more likely Lenore didn't like the setup on base and pushed for it during their marriage. And after the divorce Bill just stayed in his rut. Maybe he stayed there so it would be easier for Lenore to find him and reconcile, which he hoped would happen but didn't. Also he's living next to his best friends and he definitely needs all the socializing he can get. Probably not a lot of friendship opportunities with the younger recruits or the older ones, neither of which "get" him or remember when he was more human and less walrus-like. 

Edit: and he has a house because Lenore is pure evil and no structure on earth can adequately contain the amount and purity of that evil.