Be honest about it. It helps. Talking about it really does help. And if it makes you uncomfortable then it makes him uncomfortable even more because he can't even understand what's happening inside of your head. I stutter myself and have always been open about it in every relationship so far. My ex girlfriends found it cute and it was hard in the beginning but then I realized that at least I can have that one person I can feel comfortable with while stuttering. And I used to have good days and bad days. Sometimes I would shut down and they knew it. Understood it. Didn't pressure me. That felt like heaven and I really hope you'll feel that too. Good luck!