Dude, thats just terrible.
Try to find a church maybe. My religion always helps me. Try to get a job and get out as much as you can.
Try to get a hobbie. You can also go to the doctor and try to get help.
Try to find people to be friends with. Theres probably lots of support groups on the internet or in your town as well. Once you get enough money, go to high school or sign up for a community college if you've already graduated.
The more you stay inside, the more it will sneak up on you and attack you when you least expect it. If you get your mind off of it, you wont think about it, and if you have friends or a job and people you can trust they can help you when you're feeling down.
Just don't turn to drugs or anything, then you'll end up like your family, and we both know you don't want that.
Also, remember that you're not alone, and theres always people who can help, even if you don't know them that well. And that you do have a purpouse in life, even if you don't know what it is. Because what would be the purpouse of dying? You can be helped, so don't throw your life away now. You're only 21, and have your whole life to live. You have your whole life to learn,to grow, and to make a change. Don't let it go to waste.
I'm only 14 but if my tips can help then its worth spending 10 minutes typing.