He was always kind of off. His dysfunctional family situation just exacerbated it. I honestly do believe Chris is genuinely suffering from some sort of mental illness, personally. If I had to guess when the symptoms of that started developing it was around the time he went into college. That is when his obsession with Sonichu started in earnest, and there's that rather terrifying anecdote about him "talking" to Sonichu while in a meeting with Mary Lee Walsh.
Chris's problems all got to their current point slowly and over the course of his life, but once he left high school and truly lost most of his connections to the outside world he was left to just sort of stew in it and get worse and worse. I think the truly unfortunate thing is that Chris has needed mental help for a long, long, time. But the psychiatrists he saw always seemed to write all of his quirks off as autism, even though he's obviously got something seriously wrong with him and he's been like that for more than 10 years now.