The season 3 finale told us:
1. Locke visits Jack.
2. Jack starts to doubt himself and has a meltdown, flying back and forth over the pacific to try to recreate the crash.
3. Jack reads Locke's obituary in the newspaper during one of these flights and then calls Kate.
4. Jack attempts suicide.
It's implied that Jack had been living like this (2 through 4) for a while.
The only problem is that this new episode just revealed that the amount of time between 1 and 3 is only a few days at most. Locke dies, murder investigation, obituary in newspaper in a day or two. So a few days after Locke visited Jack, Jack grew a beard, developed a drug problem, made several flights across the pacific, and attempted to kill himself by jumping off a bridge...