Hey Brian! I can see why you are feeling down right now. You have a lot going on in a short period of time...and at quite a young age.
I don't know how much I can give you in the way of advice, but I will say I hear you and I am wishing you all good things in the days to come. It may not seem like it now, but you have so much wonderful stuff in front of you. One thing to try is
Keeping Perspective When You Have a Really Really Big Problem. Another would be
Always Look On the Bright Side of Life. Try
Rebuilding Momentum After Setbacks.
Emotoinal Mastery is a great thing to learn when dealing with monumental problems. All of these are articles that Steve wrote which have helped me tremendously. Also just try looking through the
Archives and see if you find anything that catches your attention.
I am very sure that you will be just fine, but I also understand how paralyzing the stress can be when so many things aren't going your way.
I don't know what the situation with your parents is, but you have your sister with you. Make this the time to really focus on that relationship. I don't know if you are very close, but if not, maybe you could be. As for high school friends not keeping in touch and ending relationships, those are very tough to deal with. As someone who's gone through both (and has a few years on you) I can only say that you will make many new friends and find fullfilling relationships. It's painful now, but I promise it will get better.
Keep your chin up and know that there is someone out there pulling for you. I am intending great strength (which is already inside you) and great happiness (which is everpresent -- you only have to look for it).
Best wishes.