Kudos to both of you OP! I think that it is great that you actually take your time and are willing to accommodate someone with a stutter. Public speaking is a frightening endeavour and public speaking with a stutter is even more! There are several stuttering therapies that focus on public speaking so maybe that is a focus of his. I think, as others have pointed out, that it is important that you actually ask him about the stutter and how he wants to be accommodated if at all. He is probably very aware of his atypical speech and by opening up and articulating the stutter it generally relieves a lot of tension for the person that stutter - at least that is my experience.