The posh stuff - just as an aside here, I think in some cases the alcoholic will buy good alcohol because real alcoholics don't drink fine wines and spirits/beer do they? It's a delusion, of course.
He may well be "ill" with alcoholism but that doesn't mean he doesn't understand anything, it also doesn't mean you are supposed to pretend he doesn't drink. You don't need the aggravation of monitoring his intake or calling him on it every time he drinks (because that helps no one, including you) but pretending he doesn't drink is not sustainable - because it does not serve you well.
Speaking with your close friend about your situation is not a "betrayal". Have you tried to talk to him about it? How many times over the years? What has the response been.
Alcoholism is a condition of denial and isolation. Your Husband would like you to keep this secret because if you don't then he has to face it as well and if he does that he can't cling to the delusion.
Not your circus.
Keep talking, don't let this isolate you, that is probably at the top of the list of things NOT to do, for yourself and your children, not for him and not for the alcohol, you can't let the alcohol dictate your life, you don't have to be its slave.
It's said at some point that the relationship the loved one (you) has is, eventually, with alcohol, not with the other person. Don't allow yourself to have a relationship with alcohol. You need better.
Yes, now is as good a time as any to enforce your boundaries, what are they? Seek treatment or you leave? What does that mean, does he need to go to rehab? Be sober for X amount of time before returning home?