Never ever tell him people judging him because of his stutter is in his head or treat it like it’s not a big deal when he feels bad about it. You might be trying to make him feel better that way but it never comes off like that, rather it feels like you’re minimizing it. Stuttering makes many social situations extremely difficult and people never give it the sympathy it needs. Also, if his stuttering isn’t that bad around you or if you are at the point yet. Do not start thinking he doesn’t stutter that bad, it only gets better around you since he feels safe. Understand it’s different when he isn’t around you. It’s a plus you are even asking this question. I had girlfriends who never really cared to understand it.