Completely agree, there is nothing worse than assuming someone’s preferences when talking. I am the kind of person who is more than happy to talk about my stutter to people who want to listen. Try and gage how he feels about it and definitely talk to him and ask him what he prefers in situations and CHECK IN WITH HIM in all situations if possible, see how he feels (without pushing him too much) and how he wants to go about introductions and interactions with others. It could be a good day or a bad day and you can never assume. You seem like a sweet person and as a person who stutters, thank you for taking the time to put effort into your relationship :)