Depression Support Group
Depression is a real and debilitating condition that is often misunderstood by family and friends. Its meaning can range from a prolonged period of sadness to an actual mental illness with specific symptoms. Find and share experiences with others who are going through the same struggles.

Read Eckhart Tolle's book, "The Power of Now". Consider starting training in martial arts - they are the most reliable anti-depressant, anti-anxiety "drug" out there.
And no, you're not particularly unusual or evil for having what you describe as "horrible scenarios" flashing through your head. Those are created by existential anxiety, and general disdain for the harshness of this world.
Find ways to survive and adapt. Teenage years are not representative of your life at all. Don't make any sweeping decisions about your existence.
My teenage life was torture.. pure torture.. Looking back it's truly amazing i survived.
I have to agree with some of what people have said here.
1. dont withdraw from your friends.. whether you believe it or not they care.. I know it's hard listening to people who have seemingly normal lives when yours is tormented, but listen to them.. appreciate their lives and hardships for what they are.. and when you are ready.. you can tell them about what is going on with you.. it's not a burden.. it's not bringing them down.. it's you.. asking for help from your friends.. even if that help is just a few minutes of conversation about nothing.. or a movie .. or whatever..
2. Adolescence SUCKS.. it sucks it sucks it sucks.. for everyone.. it's an adjustment period between being reliant on your parents and living the lives they live (or they want you to live) .. and you finding out what YOU want out of YOUR life.. and it IS your life.. It doesnt have to be horrible.. painful.. or awful. the human brain isnt fully developed until around age 25.. so until then.. force yourself to look at the good things you have.. even if they are minuscule.. and decide how you can make those good things BIGGER.. and a larger part of your life.. You have time.. you have control.. and there is help out there for you to get you where YOU want to be.
I didnt really start living MY life until i left for college. then it took me a few years to recoup from the damage my family caused.. then another few years to decide what i wanted to do with my life and how i wanted to live it.. but it was SO worth it.. just to be me..
3. Being alone sucks.. and it's scary to be alone.. but you dont have to be.. ever.. There are always people around who will care about you.. to be honest.. MOST of them will be temporary. I had friends in high school.. then lost them when i went to college.. had to make new friends there.. lost them when i graduated.. had to make new friends in my 20's.. lost them when i went to grad school in my 30's and made new ones.. etc.. relish the time you have with them while they are there.. you may have 1 or 2 people or even some relatives that last more of a "lifetime".. or you may not.. experience all kinds of people from all walks of life.. get to know them and understand them.. help them.. let them help you.. and dont fear the day when they fade because if/when that comes you will have room in your life for someone new.. a new experience.. a new life to learn and grow with.
Sorry everyone i tend to ramble. but I hope this helps.. dont give up at this stage when the game is just beginning..