It sounds like you are engaged in "monitoring" this man's alcohol use. That'a sensible thing for anyone to do with someone they are just getting to know. So you monitored and came to the conclusion that he has a problem. So now you are "monitoring" in hopes of seeing this problem alleviated. I recognize the pattern because I have "been there, done that." It took me down a very frustrating path. Eventually, I got involved in Al-Anon.

Al-Anon knows all about people like you and me - those who "monitor" another's drinking. I suggest you at least get some of their literature. I was surprised at how they knew all about what was going through my mind. And they foretold that I was going to expend a lot of effort in going in a futile direction. They were right.

What difference does it make whether tapering is a good idea, or isn't? Suppose it's not. What are you going to do about it? Are you trying to devise a program for this man?

So you have a goal that he should quit before his drinking "gets out of control?" He's already out of control. What you're describing is not social drinking. "Spree drinkers" are responding to a compulsion. This is not free choice. This is "need." Compulsive drinkers - which he is - are not motivated to change, until they face unhappy consequences to what they are doing.

You are trying to figure out how to solve a problem that isn't yours to solve. The more invested you get in that, the more he will hide his drinking from you.

I understand that you want to be a supportive friend. I'm not opposed to being friends with a person who drinks excessively. Go ahead and be his friend. Tell him you will be glad to help him in any way you can. That's all fine. But you sound like you are ready to sign on as his personal life-coach. Forget it.

You're trying to reinvent the wheel. There is vast expertise on alcohol rehab already out there. This guy knows all about where he can go for it. He's not the first drinker to hope he can "taper down" to a reasonable intake. That's a well-worn path. Go to an AA or Al-Anon meeting and you can hear all about the "taper down" approach.

I just googled it. Here's a link: Self-tapering from alcohol: Dangerous or harm reduction?

Do a search and you can find lots more on the subject.