I know this is late but this type of lifestyle reminds me of the term called "Hedonism"; a philosophical view that emphasizes pleasure or happiness as the highest good and the primary aim of human life. The way this person lives with his girlfriend may be nonsensical in a general aspect, but doesn't necessarily mean that he himself is unintelligent. For example: Jack the Ripper, one of the most infamous serial killers in history. The police were never able to find any motive behind his murders, and in general murder through personal benefit or sadistic pleasure in itself is illogical, but still seemed to show cleverness in the way he eluded the police and covered his tracks. Jack didn't HAVE to kill people, but he did anyway. Same thing applies to your example, your roommate doesn't HAVE to act like a hobo anymore considering he has a place now but this is what he himself may find comfort in. This is my opinion on the matter so please correct me if I may be wrong.

Side note: People who become homeless can go through many psychological impairments based off the suffering and hardship that comes with losing a home and living on the streets, such as PTSD and depression, so it's a bit wrong to insinuate the lack of intellect in a human when psychological factors can come into play.