What's this a sign of?

I started dating a guy about a week ago and we're living together. We met on a dating site and we both have facebooks. I've changed mine to in a relationship, but he refuses to change his from single. He says he doesn't have time but when I mentioned that to my ex he said that it takes like 2 minutes and any guy who won't do something as trivial as changing his facebook relationship is hiding something. Do you think he's ashamed of me? Or maybe he is doing something behind my back?