I am kinda reminded of a story from my old philosophy textbook, in which a ethnological researcher went to live with a religious commune in the middle of the Desert. All was hunky-dory and the research made friends with everyone in the commune.

That is, until one day, when the entire community turned on him and threw him out the door.

And in hindsight, the Researcher said, it was because by living with them he essentially learned everything there is to know about the religion and essentially because a better disciple than everyone there. BUT, the research never for a minute believed in their religion. And apparently, the cognitive dissonance generated by these two conflict facts finally pushed the commune over the edge.

Now, this is going to get insufferably psychoanalytic and I might be completely wrong. So take what I say with a large grain of salt. The extremely devote have a tendency to be afflicted by the condition of "isn't it obvious?" Which the more charitable might call "divine knowledge" and the less charitable call "circular reasoning due to extreme lack of outside input." Judging from your friend behavior, I think he losing certainty and is trying to seek validation to shore up his faith. And now your presence turns into a living proof to your friend that he may be wrong. And I guess he is having trouble dealing with that fact.