I see the love you have for him but knowledge is key....the reality is he is already putting his life at risk. It only takes ONE bad night of excess for acute alcohol poisoning to occur, and unless you are a paramedic, nothing you will do can save him from that.
I am a normal drinker (whatever that means) and I do not aside times for the sole purpose of getting drunk. There isn't anything baffling there. If I did that, I would no longer be in the 'normal' catagory, I'd have a serious problem.
The term 'functioning' is misleading. It doesn't make the risk or danger to his health any less because he can hold a job. There is a difference between a 'good' relationship and a 'healthy' one. Getting along great with someone doesn't necessarily mean that the relationship is healthy.
Glad you are really thinking about this because there is a lot to learn and so the more you can inform yourself, the more realistic of a picture you will have.