I really miss my dad, i don't know how to cope?

My family life may be complicated to some, but I wouldn't change it for anything. I'm 17, I have 2 sisters and we all have different dads. My little sister alice who's 7 was my stepdads daughter, but me and my other sister were treated no different, he loved us all equally and would do anything for us. I live with my nan, my mum lives round the corner and my stepdad lived down the road. I saw him almost every day, and it's so hard still living here because everytime I walk down the street I'll have memories of being with him, and it isn't easy. He died on 23rd Novemeber 2012, at the age of 36. His funeral was a month after his death, and only 3 weeks ago we found out the cause of death. I have repeating nightmares about him, and it's draining me. I feel like I have nothing to live for. When does it get easier? it isn't any time soon. I just remember seeing that hearse, picking out the flowers to go ontop of his coffin, I rememeber everything. I remember all the good times I had with him. I'm so thankful for my age, because the past 3 years because instead of him just being a dad, we were able to become such good friends. We'd get drunk together, I'd go up to his house and have such a laugh with him. But I'm finding it too hard to cope, I'm crying as I write this because I just want him back. and it's pointless, because nothing can bring him back and his death keeps hitting me over and over. I remember going down to his house on the night he died to see his mum - people were there, his brother, his family. What I didn't know as I was about to leave the living room, was that the body was still in the house. and I ran out, he was upstairs and just about to be brought down. That's something that I can't forget. It makes me feel so sick. I guess what I'm trying to ask is, when does it begin to get better? does it get easier? does the pain go? I want everyone to know what an amazing man he was, he'd always have you laughing, but it just kills me inside to know that it's forever gone. I know that's life, people die, we all die eventually. It's just affecting me so much, I don't want to leave my bed, I'm so depressed. I'd like to leave this world and be with him. I'd be happy to die, I can't wait. I'll feel no more pain, and I can be with him again.