Perhaps he feels as if he has been spending too much time with you. Encourage him to hang out with some buddies to get some 'guy time' in. It's a healthy thing for relationships. It's also fun to do social things together, even if you don't know anybody else where you will be going, like to the bowling alley. If you do something like this, invite his friends as well as some of yours sometimes too.

He may well be wanting attention. Name all of his friends, and he will come to see he has loads, or say that you have none and he will now what it feels like to be you.