I can't stand it when threads get shouty.
Abbdabb, I'm delighted to see you came back to your thread but wouldn't blame you if you imploded while reading it ...
... I'm also guessing you wouldn't have liked some of the things I posted earlier on, where I made some assumptions about the kind of character your H is. I based my assumptions on life experience, but I have one scientific fact for you: some people really do enjoy super-efficient alcohol consumption. It's to do with the combination of alcohol-processing enzymes they have - which is genetic.
The 'efficient' combination is more prevalent in Nordic types and those descended from tribesmen of the Russian Steppes, though it also turns up in some people of African heritage. Additionally, this set of genes mutates fairly quickly - someone from a long line of very hard drinkers would be more likely to have the genetic ability to metabolise alcohol quickly. The downside of the 'efficient' enzyme combination is that it makes liver disease more likely (due to the by-products they release on processing alcohol.)
So there's your genetic bit about why some people really can show lower-than-average blood alcohol levels after drinking.
The other part is purely observational. You'll have to trust me when I tell you I have known a lot of charismatic, successful psychopaths who display a phenomenal ability to engage in addictive behaviours without getting addicted. It has been medically noted that psychopaths have a very high pain threshold. My unscientific theory is that the shutting off of parts of their brain (which is proven) interrupts the links between physical sensation and emotion. Ergo - unscientifically - socio/psychopaths both crave more 'excitement', in order to get the buzz, and are unattached emotionally to those excitements. They can seem addicted but, in fact, make a free choice every time and can stop on a pinhead. My guess is it's something to do with neurotransmitters, eg dopamines.
So, anyway, I've allowed my past familiarity with psycho/sociopaths to paint me a picture of your H not as an alcoholic, but as a boundary-pusher with the inability to care very much about other people. Whether thinking about the children he might hit while driving a bit pissed, his own children, his patients or you, I suspect he really can't care very much because he really can't see them as actual people with lives. I suspect he feels kind of empty inside but - far from using alcohol to numb that pain, uses it to get some semblance of feeling. I asked whether he abuses the drugs at work because I've known quite a few dentists who did exactly that - for the same reason; to 'see what happens'.
Indulge my ramble, please. I'll be interested to hear whether you think your peripatetic H is like the hollow-souled charmers I've known :)