I'm deaf, and my girlfriend has a stutter. From what I've gleaned from her, and studied in my psych classes, stuttering can have many causes, but the biggest one is clinical anxiety. There's not much you'll be able to do other than just be a loving Spouse. And honestly, I think all he wants from you; not to be treated differently. A disability is not a single ounce of a reflection on who a person is, and the best thing to do is just to embrace that as part of who the person is. Hell, my GF learned ASL just so she could interact with me in my language. If your fiance opens up to you about his stutter, embrace it, as I can't imagine it's something that's easy to talk about. I would recommend trying to get him some professional help (either a therapist or speech pathologist) ONLY if he does talk about it. You seem to have a fantastic view, and I wish you all the best!