How would I go about it?

Here's the story: I have a near impossible exam in 2 days. Professors say that this is the one that determines if we'll become doctors or no. I am near certain I will fail even though I will try my hardest not to. I've been thinking about suicide a lot these past years, almost every day. But this week, when I was drunk I was ready to do it, luckily I calmed down. Today, I came up with a plan for doing it. It's getting too real. If I do fail this exam I will overdose on my anti-depressants which I have left from earlier treatment and I will slit my wrists. And no, it's not because the exam even though the only thing I've wanted was to become a doctor I could be without it IF I HAD ANYTHING ELSE. Which I don't, I am completely alone in this world, I've got no friends or any positive outlook towards the future. My father is a drunk, a complete retard. Probably the only person I would feel sorry for is my mother when she finds out I'm dead. Last time I saw her I told her that she is the reason why I'm so alone, it isn't true, the real reason is my father, my own fear to do anything. So I am asking you, what do I have to live for? And don't tell me that someone will care if I'm gone. There is nobody, I am so very alone in this world. Don't tell me things will get better because they wont. I saw a therapist for a year and the only thing I learned there, was that we are who we are and we can only change the way we behave. So right now I'm sticking with my plan. The exam will be a sign for me. People say it's the hardest exam of them all. If I don't fail I'll keep going, but if I fail in the exam, I will fail my life. Sure I could re-take the exam but why bother. I'm useless at this, I study way harder than most people and I still get low grades...