I am not a psychologist but I can try to give you advice straight from the heart. You may wish to just consider what I say, you don't have to push yourself too hard to follow my advice or whatever. If you feel like you need professional help, please go to a counsellor or psychologist, talk to your carers, friends and teachers and keep yourself healthy.
Recently, I too had to deal with a very painful death in my family. But there was one thing that helped me thank the ones that have passed and gave me motivation to move on, I guess. Barley is sort of right. You can never really move on from a death. You just have to live with it. Straight and simple.
But why live if you won't see the person anymore? You could be having those kinds of thoughts. Or what will happen to me? Am I going to die too? Nobody knows the answers to these questions to be honest.
Then, what would the departed want from me? How important is the departed to me? He/She loved me and I loved them back, I am sure. What now?
Now, I think that you need to keep the mark, the essence, the imprint of the person's spirit inside of you. It may sound crazy but the love of that person to you is true and persists even beyond death. You will never forget that love, even if you forget their names and faces.
So what does that all mean? What should I do? I think you should now show your own love to the people around you. Just like your friend showed their love to you, you will have to show love to your loved ones too. It is going to be undoubtedly painful. You will always remember your friend's love. But, simply think about the future. About your own death. Not in a selfish way, but how you will affect these people when you die yourself. Once you die, you woudn't want your loved ones to fall into a dark pit of sadness, would you?
Once you get the love ball rolling, I believe that things will improve. If all of that doesn't make sense to you, that's ok. Just writing in words really isn't that effective at conveying what I'm trying to convey.
But the main message is, don't forget your friend's love and affection. Don't forget your own love for your friend and don't forget your love for the people around you. Let that be one of your motivations to drive you in life.