I feel like if he's going to mock your stutter then it almost most certainly speaks volumes that he'll be the type to already or in future, mock other disabilities or vulnerable groups of people. Like where is the compassion? My speech therapist told me this that we are much more important than the stutter. He should see that *you* matter much more than your stutter, and shouldn't break you down when he doesn't know the day-to-day struggles. He has a problem that you stutter? Don't let his problems be your problems. You can be confident, with or without a stutter. You deserve support and empathy in your relationship, not a constant bigoted bully who drags you down for something you're already harsh enough as it is on yourself, especially that he is increasing your overthinking when talking to strangers.