the pretense that was the worst thing — "he let Fackelmann fix them both…"
he let Fackelmann fix them both up but good, and told himself he was doing it to keep Fackelmann company, like sitting up with a sick friend, and (maybe worst) believed it was true.
Context
The anatomy of a relapse, told from the inside with no mercy: the desire "that blots out all bother" rises "so automatically" that Gately is up out of the bed and lumbering toward the corner before he's registered a decision, wrapped in a cover story pitched not at anyone else but at himself. The worst part isn't the using — it's the pretense of tending a sick friend, and worst of all that he believed it. This is the self-deception the program spends its whole apparatus trying to strip out: the addict as the one person he can always con, the story that lets the hand pick up the works.