It's hard to accept a death you don't understand. I am so sorry you lost your friend. My condolences.
Grief has its own timetable. I lost my mother when I was 12, and it was a long time before I could talk about it. My father-in-law passed away last year at 87, but it was an easy death, and it was his time to step off the wheel of life. My husband and I were a little sad, but also relieved that he wasn't suffering anymore. He was just so TIRED. It was his time.
I'm going to take a chance and assume that the friend you are grieving for was young, way too young to die when he did. That's hard when someone is snatched away from you, like your friend was to you and like my mother was to me. Sometimes there is no understanding death. It just happened.
But I'm convinced that we all go when we are supposed to go, even if it makes no sense to the survivors. I have a theory that you come to this life with some things to learn and accomplish, and once you do that, you can check out early or you can keep on living. But this is just my idea. Maybe your friend did what he came to Earth to do, then checked out again. Maybe his soul is waiting to be reborn, so he can come back and help others and learn even more. Maybe he is done with being human and is able to move to a higher plane of existence? It's all speculation.
A good thing for you to do is to talk to someone, like a minister, priest or rabbi, a trusted teacher or counselor, your good friends. Talk to your family and to his family -- but only if they are open to talking about him. They may be going through their own grieving too. Keep a journal. Write letters to your friend. Tell him about your days, your thoughts.
Go to church or synagogue, light a candle, say a prayer, or whatever your particular faith is. A little letting-go ritual, no matter how religious you are or not, would probably be a very good thing. I'm sure you can do some research online or come up with your own personal letting-go ceremony that would feel just right.
Remember grief has its own timeline. Often the people we grieve for the most are the people that we have unfinished business with. Maybe you really liked this guy but didn't tell him your (possibly romantic?) feelings, and now it's too late? Learn from this, and tell people that you care about them, because in the case of your friend, sometimes it is too late and we can never again tell people that we love them.
Also, as soon as you are able, get back into the swing of life. Join some clubs, go on some dates, go to movies, exercise, eat right, get enough sleep. The ache in your heart for your friend will never go away completely, but over time it will lessen.
You're a sweet and kind person to care so much. I hope this helps. Good luck working through your grief. Take your time and heal yourself on your own timetable.