Parents, as a rule, are hesitant to allow their offspring to embark on an alcohol-fueled campaign of self-destruction. According to British advice columnist Virginia Ironside, this is a mistake. A son's raging alcoholism is not something to be "pitied" or "treated"--the little rummy just needs some support. Explains Ironside:
(Hat tip: The Awl)
Get this idea of "denial" out of the way. Very few people are in denial about anything, when you get down it, particularly drinkers. Presumably your son is not a blithering idiot. He must know there is a strong connection between his losing his job and his girlfriend and his drinking. At the moment, however, he would just prefer to drink than not to drink. He prefers drinking to a job and he prefers drinking to his girlfriend. There is no denial going on here and to suggest there is seems rather patronising. Give him credit for making a deliberate choice. It may not be the choice you would make, it may not be a sensible choice, but it is a choice and he has made it. If he wanted to give up drink he would. But he doesn't want to at the moment and there's nothing you can do to change his mind.
You, of course, would find it useful to attend Al-Anon, for relatives and friends of alcoholics, where you'll learn that the best way to cope with alcoholics is not to do their worrying for them. Don't pick at him. Don't throw drink away or make remarks about how horrible he is when drunk. He knows.
In the meantime, look at the advantages. He's not sleeping rough. He's not stealing. And he's actually making a contribution at home. Some parents, with lazy sons lolling around at home at the age of 30 who are stone-cold sober, would be envious of your having a son who is at least engaging with family life.