You seem to be going thru the normal grief process. There is no time limit on grief. Do seek professional help if you feel like something is not right. Also, know it was not your fault and there is nothing you could have done to prevent it. Here is an article on this site about grief:

The 5 Stages of Loss and Grief | Psych Central

I hope you can remember the good times and learn to smile when you think of your friend.