I used to do the same thing fantasizing about being "cool." I realized it was damaging because it only made my real life seem worse, so I intentionally stopped doing it (which included not listening to songs that triggered my fantasies). I suffered from the lunch time anxiety you talked about when I was in high school. Middle and high school are such embarrassing times for anyone, especially people with social anxiety. I think every year my social anxiety gets better just from being exposed to more situations and getting further and further from that teenage self (I'm 33 now). I journal a lot about my negative thoughts and try to reframe them, but I still have them narrating my life most of the day. I have felt suicidal for the same reasons you talked about. But then I am so scared of dying, like not existing, that I figure even a very hard existence is better than nothing. And knowing there are TONS of people going through what we go through. Humans are resilient. There is a lot of joy still to be found in solitude and even in relationships when you find people you are comfortable with (which it sounds like you have through the army). Stay strong, friend.