Stuttering runs in my family. I stutter and passed it down to my daughter. My son doesn't stutter. My stutter is mild. And my daughter is also very mild. However, she seemed to grow out of it by the age of 15 and tells me she doesn't stutter anymore like when she was younger. I still stutter though, but extremely mild and I have learned to accept it, it flares up sometimes. There are so many things you can pass down to your kids. Anyhow, do some more research and see how easily passed down it was for your bf's family. Maybe talk to him about it also and your concerns, maybe he has the same concerns.