I quite understand what you are going through. Majority of the people who stutter have same issue. We can speak well with friends and family, but can't utter a word to others.This is mostly due to fear of stutter. From my experience best way to reduce this fear is to be more open about it. Whenever I am in a nervous situation, first thing I do is to tell them about my stutter. This puts me and listener at ease and greatly reduces my fear. Try to be more open and accepting of your stutter, I am sure you will feel more relaxed. If you are looking for some outside help, I recommend McGuire Programme. It has greatly helped me to control my stutter.