Sorry to learn about your friend. I know you will struggle with it for a while.
In 2020 I had 3 long time good friends die suddenly for different reasons. I struggled with emotions from each death. One of them, I have thought of every day since their death.
I got some professional counseling through my medical coverage and I read a book about dealing with death. Both helped. You might want to consider one or both of those my friend.
While I fully appreciate the sincerity of your post, I am doing quite okay. My point wasn't about my own mental health, but rather that we don't know how long we are going to live so we should enjoy our lives within reason because getting old isn't guaranteed.