I had this for a few years in my twenties. It was horrible, so I can totally empathize with you. It finally went away when I started getting more confidence in myself and stopped seeing the world through the lens of a scared little child. When I started seeing myself as an adult (and especially when I noticed situations where I was literally smarter than those around me), I realized how pointlessly self-sabotaging this fear mentality was. I also took noticed when other people would stutter (sometimes badly) and they didn’t let it destroy their self esteem like I did. A few small-but-significant changes in my thinking made my speech problems go away quickly and completely.