In the book, written long ago, mind you, it's made pretty clear he is a closeted (of course) gay man. Back in those days, even in a big city, being gay was illegal, dangerous, to be denied and hidden as it made you despicable to society. Surely his inner stress and self-loathing contributed heavily to his self-medication with booze.
shareWow, never knew that, makes me want to read it. IDK if it's in the book, but on top of all you just stated as reasons for his drinking, imagine his terror at wondering if he let his secret out in a blackout!
Just as I was typing the above paragraph, the part in the alcoholic ward came on - is Bim the nurse a gay man in the book, possibly sympathetic to Don's plight? I thought Frank Faylen acted ever-so-slightly fey, maybe as an homage to the parts of the book they couldn't put onscreen?
That interpretation is too restrictive. This film is made for the viewer to empathize with the alcoholics point of view and the power of addiction. While some of these demons as you point out might be psychological, we know now that there is a heavy genetic component to alcoholism.
Alcohol is completely banned in certain parts of Alaska because the native population just cannot stop themselves once they start drinking. I don't know if this ban is still enforced, as it is currently going through the courts as being racially discriminatory.