One other thought. A bad stuttering day or episode is often a surprise to the stutterer. We often don’t know why they happen. 2 main causes that I can identify for me include lack of sleep and having to talk to strangers or talking in casual groups but everybody has their own things to watch out for. I’ve heard some people identify certain foods as causes which seems odd, but maybe they’re right. But usually we don’t know why we can’t talk normally in my experience. Sometimes I can barely speak to my own adult kids for example - for no apparent reason and it can be upsetting. So that’s what he might be dealing with. Kudos to you for educating yourself about this - best of luck to you and your guy!