It's a tough situation but I will give you my experience as it relates. First in the end I was drinking around the same as he is. My wife and I would have both said , prior to getting sober, that I was a functioning alcoholic.
I will tell you now that in my opinion only , there is no such thing as a functioning alcoholic. I was going to work, taking care of most of my family responsibilities, and living life but it was at a level far from my best. I am much more productive sober.
I will say that my wife of thirty years has stood by me through all of it. I do believe if she could have seen the future three decades ago she would have ran the other way.
We are happy now but it is only because I do not drink at all ever. I do know that an alcoholic can have a rewarding happy relationship but only if they are sober.