Stutter disappears with one person

Stutter disappears with one person My stutter isn’t as bad as it used to be. It comes up sometimes when I think about it or talk to family members. And is not there when talking to myself and this one friend of mine which is weird. Ive never stuttered I front of this friend. I talk to him all the time and I’ve met him earlier this year. Why is that? And how can I maintain that with all people ?