Complete (outward) denial. He may understand it deep down, but if he can't come to the point of admitting it, then he can't come to the point of fully realizing that it's destroying his life as much as their own.
My alcoholic exbf said some of the most confounding things about other people with substance abuse issues. A good friend of his had his relationship fall apart because his girlfriend was an alcoholic. His response to it was how unfortunate it was that she let alcohol get in the way of that, and then assured me (while understanding he had his own problem) that he'd never get that way.
Another friend of his who was an addict was "a loser that was going nowhere and throwing his life away on drugs," and he was explaining this completely drunk at a bar to me one night.
Another friend who had a boyfriend who abused alcohol pushed her one night, and he talked to me about it with concern, hoping it wouldn't escalate to him hitting her eventually (a few months after he pushed me one night).
It's amazing the amount of personal denial they can have at times, and overall denial when they know how obvious their problems are.
It doesn't matter if he recognizes or refuses to recognize it in other situations - he doesn't recognize it in himself. My ex always figured he still had time before he became a full-fledged "alcoholic" and really needed to get help. His was a denial of semantics. But, denial is denial. If it's not recognized within, it's not going to be helped.