I ate like your roommate for years, and no one, no matter how well-meaning, could convince me there was anything wrong with that. Consider yourself lucky to be further along the path toward health than him. Many people don't have that wake-up call "I need to get healthy!" moment until they're already sick. It's hard to watch people who are close to us do things we know are dangerous, but our advice and insistence is not going to be what makes them change.
You've gotten some good advice on this thread; keep leading by example, let your house fill with the scents of delicious grass-fed beef and sizzling veggies and see how long he holds out then! People who make unhealthy decisions KNOW they're making bad decisions. They just think getting healthy is too difficult and inconvenient. Just keep living your primal life as proof that not only is being healthy easy, it's worth it!