I think one of the biggest problems is just being a teenager, stutter or not. Starting to plan out your life and becoming an adult is stressful enough. Stuttering only amplifies it. I eventually realized that my behavior of self isolation with constant negative thoughts was only worsening my mental health and overall fluency. It served no purpose, but I had to go through that suffering to come to that conclusion. So I would say to you, focus on your mind first. The thoughts of never having friends and constant embarrassment because of your speech are simply thoughts (among other stuff you touched upon). Sometimes we are unapproachable to people because of how visually uneasy we are about our stutter, not the stutter itself. Your thoughts do not always reflect reality, they are not always true. Do not give power to your fears. Substitute bad habits for good habits. Just try to get out of your head. Hopefully some of this makes sense, I’m kinda rambling. I’m sure you’ve heard a lot of what I’m saying, but it’s what worked for me. Not that I’m totally fluent or anything, but I’m much happier. Most importantly, just know that you are stronger than you may know. Times may be tough, but things will get better. You got this.