Another thing that you should be aware of are things that tick people who stutter off. I speak for myself when I say I hate when people finish my sentences, cringe when i’m having a hard time getting through a sentence, tell me to relax and calm down, or anything that alludes to you blatantly highlighting that i can’t speak properly. One of the most comforting things you can do is be patient, allow him to fight through the sentences, and keep a straight face/smile. a lot of people’s innate reaction to a stutter is to cringe or distort their faces which makes the person stuttering more self conscious and eventually hesitant to keep going. You being patient and showing you have time to wait reassures us that we won’t be ridiculed even when we struggle and it’s ok