Do you have a real hobby? If not thats something that will really help you. It did for me, when I became an artist.
You mentioned the military, is that even something you are interested in? I understand they wont take you, but see that as a blessing in disguise maybe. "Never work a job you wouldn't work for free", and if you would have taken part in the military because you needed to feel apart of something, you are trying to find some sort of emotional profit.
I definitely understand finding a purpose is the greatest goal one can achieve, but rather than longing to feel like you are "normal"(which is very eye of the beholder), you should look for your purpose. The wonderful thing about life, is that it can be anything. Even homeless people can enjoy there lives!
No offense, but if your brother is really that much of a prick, he's probably a dipshit, and most sane people wouldn't like to be around him for more than five minutes. I recommend ignoring him. But he's family? you could ask, haha shouldn't he be asking the same about you? And if he doesn't, he obviously doesn't care, why should you?
Sorry the first part was directed at both of you, the later parts - Number 6.