Quite possibly it's the beginning of the end for your friend. I know the df'ing certainly was for my friend. Sure, he went back all gung ho about doing the "right" thing... but those months of sitting there through meetings without a friend in the (non)world finally started to get to him. The doubts, the loneliness and the confusion started to eat away at his enthusiasm for getting back into the group. When you've got noone to talk to you have plenty of time to think... about your so-called friends who won't have anything to do with you... about your bottom-shelf worldly friends who still love you despite it all...about those points and doctrines you really couldn't fully accept. For my friend, his zeal for witnessdom started to dwindle. And then one day, months later he decided he didn't want to be a witness anymore.
This could be the beginning of the end. My advice... be available to help but don't overdo it. This newfound ardor will run it's course. In the meantime, don't allow the double-life scenario of allowing your friend to use you as cut-rate crutch while he saves his best for the "good" folk in the group. He's got some lessons to learn- give him the time and space to do that.
You still love him, huh?