I can understand that actually. As long as you are very clear in your boundaries - you know what you will and won't tolerate (for yourself), it isn't a problem really is it.
Even if he confesses the extent of his drinking - it probably won't make any difference.
I see it this way. A person can choose to go all in - as in this person is an alcoholic and I am choosing to be around them. I accept their drinking to excess and all that accompanies that (hangovers, not wanting to go out, having to drink before every outing, mood swings etc etc).
Although, just because he is struggling with addiction doesn't mean you can't call him on anything that's outside your boundaries - like him taking a bad mood out on you etc.
I don't see a problem with that unless it starts affecting you in a negative way. If you find your self esteem isn't what it was (being ignored can do that), your self worth isn't what it was. You find yourself worrying about him when he vanishes (which you mentioned). I guarantee you he will be ok, or he won't, he might end up in jail - but your worrying won't help. He was drinking before he met you, this is new to you but not to him.
The other thing to keep in mind is that alcoholism is progressive. The amount he drinks now and its affect on him may not be that way 6 months from now or a year from now or heck a week from now. Addiction is not stable like that.
You have never known him as a sober person and, depending on how long he's been drinking, he may not even know himself as a sober adult. So even if he chose to get sober (which isn't on the table right now), you don't know what he will be like (neither does he). Getting sober is one thing, getting in to recovery is a whole different thing.
Sorry for inundating you with all this info at once, I'm neither trying to talk you in to anything or out of anything, just that the more you know about alcoholism, the better (for you, not for him)