This is the case for most stutters. Most of us can speak fluently when alone, but stutter in front of others. A therapist I used to work with would say "what if you were reading aloud in your room and someone suddenly popped out from behind the couch, would you immediately begin stuttering" Why? This example always made me laugh, but when we stutter we are giving others the power to control our speech. We need to realize we are the ones in control. It's about changing your mindset. Why do we let someone else control our speech? What gives them the right? Reading aloud, positive affirmations, and intentionally stuttering helped me a lot with this. Intentionally stuttering was so hard to do for me, but it really didn't help to reinforce the fact that I am the one in control and not someone else. Hope this helps.