If it's getting to you to such a point that you're feeling terrible within yourself, it's fine to text a friend and say 'Sorry, I'm going through a really hard time and can't be around people right now.' A true friend will understand and accept that, and still keep contact unless you ignore them or push them away. Having said that, avoidance can become pathological (I actually have Avoidant Personality Disorder), so it's important to keep doing the things you want to do. Socialising when you have a severe stutter can be really difficult, but not socialising at all will have detrimental effects on your development as a human being. So you need to find a way to deal with the feelings that prevent you from living life. Cry, rage, run around, psychotherapy, creative projects, whatever helps you process those emotions, even if it's painful, do it. Wallowing in misery will not help; I did that for far too long. Find a way to live, not just exist. You can do this.