I know it hurts. That's life. If nothing else, It's life. It's real, and sometimes it f*cking hurts, but it's sort of all we have. you arent selfish. the world isnt fair. I know how you are feeling and i know that words are hardly comforting but just know that you arent alone. And life is f*cking hard....i see your the same age as me...and us being only 17 we dont have a lot of power to change what is happening in our lives. But hang in there. Things seem bad, but they always get better at some point. I could be completely wrong, but i think you once said you were into photography...this might seem lame but have you ever tried taking pictures expressing how you feel? One time when I was feeling really awful and suicidal I walked down the road with my camera and took a picture of flowers stuck in the mud and things like that. and i dont know, it kind of expressed how i felt and then after i took a bunch of pictures i kinda felt better.
But hang in there...good times are bound to come.
You hang on by taking each moment as it comes.
If you get really desperate then you need to go to the hospital.