That too is a possibility, but not a certainty. That is exactly what makes these things so hard.
> As you noted in your first comment, maybe "he's drinking because it brings out the brother in you".
Yes, but I have absolutely no idea if that is the case or not, and even with my own brother (Maurice, 12 years my junior) I'd have a very hard time to figure that one out. Let alone that I could know which way that coin landed for someone else. I haven't a clue, to be frankly. But I thought that saying that might open the OPs eyes to some of the weirder possibilities.
In the end almost all addictions are a from of escape, the question is from what and why and if it can change, and the first step will have to come with recognising there is a problem, which for the moment the OPs brother does not seem to agree with. So that makes it a very complicated and tricky situation.
Unfortunately alcohol addiction is a subject that strikes pretty close to home for me and I could tell you some stories that would make your hair stand on end. This also means that I may not be the most rational person when looking at this as an issue, personally I'm instantly more worried about the brothers nearest family (wife, kids and so on) than the brother himself. Scars like that heal only very slowly.
The 12-step world has all sorts of theories about these behaviors, under the titles "codependency" or "enabling" or "rescuing" or "detachment". I can't say for sure whether they're right but someone struggling with these issues, like the OP, may want to familiarize themselves with that literature. A reasonably-sized bookstore will have a large section of books about dealing with alcoholism, as a drinker/alcoholic/friend/child/sibling/parent/spouse/adult-child/stepsibling/etc, in every permutation.