I'm really glad you are one of the good ones. Us stutterers are very humble, kind and patient. Some good tips are to wait for him to finish sentences (even tough it might be awkward just standing there lol), please don't bring up his stuttering, as you should let him initiate the issue. Always make sure to comfort him when he is feeling annoyed by his stutter, which will lower the amount of stuttering he does. Thanks, and good luck.