Murky - I'm not sure who you have sought help from, but have you talked to your GP? You are free to go and make an appointment without your parents accompanying you if necessary. Please tell your GP that you a feeling suicidal and are seeking the means of trying to end it all. This will help him/her understand where you are emotionally and enable him to find the best means of support for you.
It sounds as if somebody has let you down very badly, and you are possibly now suffering from a deep depression.
Would it help to know that most people at some point in their lives feel empty or overwhelmed by something horrible which has happened to them. It feels like a bereavement where you sense there will never be any joy or laughter in your life again. But slowly the light does come into your life through small incidents and the support of friends and family.
Can you share your problem with us?. There are a lot of people here who will understand your feelings and try to help you. Why don't you just put on a jacket now and go out for a quiet walk ? Look around you. Listen to the birds. Look at the flowers and the trees and try to calm your mind. Try to think about all the good things which have happened in your life so far. There will be plenty more of them to come. What it needs at the moment is being patient and takingt one day at a time.
I have known a few people whose relatives have committed suicide. I can tell you that in every case, the death of their loved one has left them feeling totally devastated and left an emotional scar which has never healed. So , even if you do succeed, you won't have gone quietly without fuss. Please do share your feelings with your family, some close friends, a neighbour, or your GP. Or, if you can't face them, come and share your problem with us.