Oh, without a doubt Ed is ultimately the one responsible for his drinking problem. I mean, a person can allocate exterior reasons for why they feel they have to abuse alcohol, booze, food (being sexually abused/beaten as a child, etc.)...but I honestly feel there reaches a point where a person is grown up enough in terms of age to be held totally accountable for the way they choose to respond to whatever happened to them as a kid. I think in Ed's case he simply liked to drink and get drunk because he enjoyed the way it made him feel.
I think Al was just in denial about it for a long time. And I wouldn't discount that perhaps Ed has been a bit screwy in the head for a long time, but signs of that didn't start to physically manifest themselves until after his cancer scare and the failure of Van Halen 3. I mean, you look at the choices the Van Halens made from 1996 onward, and it's like they were a bit cocooned from reality. It wasn't until Van Halen 3 bombed, then Warner Brothers dropped them, then they filled their coffers with the Hagar tour in 2004 and after that I think Ed just went off the deep end after Valerie finally left him a year after the 2004 Hagar tour was over.
I think (I don't know for sure) what it came down to was that Azoff was either told by promoters they wouldn't be giving Van Halen any guarantees in 2007 or that Ed couldn't get insurance in 2007 for a tour unless Ed could demonstrably show he was clean and sober. I think it came to that point and only when that point of Ed's behavior possibly affecting Van Halen's ability to tour and earn was reached (along with some other Ed health problems)...the realization finally hit home. Because you look at those pics of Ed in late 2006/early 2007 with Roth and Ed's appearance at the late 2006 NAMM show, and Ed is still clearly fucked up. And when you live with an addict as long as Al has lived with Ed, you only stick around if you learn how to accept/rationalize/make excuses for that behavior. Otherwise, if that person makes a choice of engaging in a harmful addiction over your friendship and you find that intolerable, you eventually walk away if you have any self-respect.