Mal shared a theory once, after the Bruce Vilanch Unmasked post-show, about her thoughts on Fez. It was very in-depth, and I can't remember all of it - I doubt I'd do it justice anyway.
But the gist of her point was this: here was a man who lived a character for decades on the air and to fans, and was a different man in his own personal life. The former, Fez, was a boisterous queen, campy, charming, controlled a room and an equal to Ron. The latter, Todd, was quiet, riddled with anxieties (keep in mind, this was a man who after the 9/11 tower strike turned to Ron and said "why do these things always happen to ME?"), and reclusive. Then one day, Todd realizes he was much more like Fez than he cared to admit, especially in being gay. That caused a crisis of conscience, as all of the flaws and anxieties of the private Todd came to the surface through the public persona of Fez. The happy-go lucky, Fezzitorial-spewing second mic became Mr. Quiet In The Corner because, at this late point in his life, he struggled to come to terms with who he really was.
He was too set in his ways and too comfortable being two separate people that he probably couldn't figure out how to make it as one whole person. Now that he couldn't be an act anymore, all there was to be was himself, and he didn't know who that was anymore.
Christ, remembering all of that made me sad again.