Hey that sounds like me! I never considered myself an alcoholic because I didn't drink everyday, and if need be I could take a few weeks off no problem. My only issue was once I started drinking I didn't have an off switch. I'd stay up until 3-4 a.m. drinking, watching sports highlights, videos, reading stuff on my phone by myself. I was never an angry drunk, I was almost never visibly drunk even when I knew I was wasted. I was a great drinker and kept my shit together and did awesome at work. I told myself no harm no foul. My wife would usually deal with my sleeping in until noon after a heavy night and not say anything even though it was a dick move honestly.
What I didn't tell anybody was that every single hangover I had always came with thoughts of killing myself. I was drinking to mask depression that I never wanted to address. In the morning it would always hit me at once. I kept it to myself, I was super nice to people, and from an outside perspective I was doing great, but I was definitely an alcoholic.
It's a touchy subject. I'm in my 30's, and at the time I would've denied any problems I had. He probably will too, but it's a real issue and you have a right to be concerned. Those are the actions of a depressed person, and he may have it under control now but that won't always be the case. Ask him about it, tell him you're concerned and don't accept "I'm fine" as a response.
Ultimately addiction is in the hands of the addicted. You can deal with it until he decides to get better and that is your only option honestly, or leave if it gets bad enough.
I still have issues, but I've quit drinking and switched to weed. Now I'm in bed at a reasonable time and have to work on my new cereal addiction.