I am so sorry, truly. You are so young, and no one should have to go through such a tragic loss, but it's harder when other people your age haven't had an experience like this.
How long ago did this happen? It is perfectly OK to grieve your friend's loss. It would be abnormal if you didn't. The loss of appetite and wanting to sleep is also very common with people who lose someone close to them. I just don't want you to let it go on to the point where it damages your health and emotional well-being.
I'm sure it is hard to talk to other people, but have you considered talking to your school counselor? Or are your parents concerned enough to get you a private counselor? They can be really good at talking through the grief. It sounds odd, since they are strangers, but counseling can be really helpful in moving forward with your life.
You are so young - please don't consider joining your friend. You will never forget him, but you WILL have good time ahead of you, and so many experiences and opportunities are waiting for you.