Hello mls:
It sounds to me as if a lot of what you're going through is a combination of the usual uncertainties one can have when they're stepping out into the world on their own as coupled with grief. In other words, all things considered, it's normal, even if it does suck mightily.

It sounds as though you lost a good companion when you lost your stepbrother. This was someone who seemed to make you feel accepted for who you are and also seemed to appreciate your unique qualities. That's a big loss and those kind of losses take time to move beyond. It's not unusual to feel intense sadness and a lack of passion even a few years after such an event.

Grief can also be more difficult for a male in this culture -- women cry, they hug, they express themselves and they get their feelings out. Men are more inclined to swallow their feelings, especially if they don't have anyone they can share them with. To actively grieve men often need to do something, to take action in some way. It might help you to come to terms with your grief if you develop some grieving rituals. Here's a link that might be insightful for you in regard to men and grief: A Man's Grief

As for your lack of social circle... I've found that the best way around that is to find some things that you really enjoy doing and then go do them. If you've ever wanted to learn how to play guitar, or develop photographs, or climb mountains... this is the time to pursue those interests. Often, we cannot let go of our old way of life until we have actively sculpted out a new one. Doing new things is one way of sculpting. Somewhere in there you are bound to encounter other people who are also doing what they enjoy doing. This mutual enjoyment can be enough to forge a friendship and it sounds as if that's what you most want in your life right now.

Meanwhile, be assured that all those other people you encounter on a daily basis who appear to be so unruffled and confident on the surface are probably very much like you under the surface. All of us have doubts, all of us have inadequacies, all of us have wounds -- this is part of the human experience. In learning to accept your own humaness, you learn to accept the humaness of others and this levels the playing field dramatically.

Somewhere out there are other people who like the same music you like, who you get the same jokes you get, who like to do the same things you do. Go find them and when you do, remember that they're just as human as you are.