I think this would be a really valuable fear to share with your therapist in order that you can explore what's going on for you now and simultaneously how it reflects your childhood fears. It sounds very much as if you are describing your feelings about your mother: if I am honest with her or if I assert my true self, will I be too much and so disagreeable that my mother will leave me? If my mother rejects me, I am alone and I am in danger. These are archetypal fears and ancient dreads.