I feel like he is being insensitive to you. If you're clearly struggling and having a hard time and he's still not taking it seriously, then he sounds like a d-bag. Don't make an excuse for him on this - even if he doesn't know what it is like to struggle with speech, he shouldn't be laughing if you're on the verge of tears over it. It's a hugely personal issue for people and you are not being insanely sensitive about the topic. I was with my BF for over 2 years before I finally opened up to him and told him about how much of a struggle speaking is for me and how stressful it is in my life. Doing that was one of the best things I ever did for my speech and he's been the first person I let myself openly stutter in front of (now there are a few - yay speech therapy).