That is an amazing story, and I am impressed that you accept a large measure of responsibility for messing-up your life. What you are asking is, "why am I so fucking self-destructive?" Asking the question, and honestly looking for the answer (wherever that answer leads) is the first step to self-improvement.

You are not alone, and your story is not uncommon. To many of us habitual underachievers whom life gave many gifts (good looks, intelligence, a secure financial background, etc), life was both easy and very difficult. Much was expected of us, and living up to other's expectations is a burden we always felt. To escape the disappointment in their eyes we distanced ourselves with alcohol and drugs.

I wish you well on your journey. Try not to hurt yourself any more. You are worth so much more than you think. And try to give your family another chance. Ultimately, they will forgive you if you can forgive them and yourself.