Sorry to hear this. I lost my very closest friend a few years back in 2017. The grief was unreal and in many ways worse than losing a parent. The only thing that helped was to be thankful for all the good times we had, and to tell the best stories. Initially I really wanted to try and find another like him, but that was silly, he was quite different and amazingly capable. A 777/787 senior captain for American.
Make sure to be thankful for the time you had, and that you had as much time as you did.
EDIT: I've lost a large number of friends in recent years. In fact, all but one of my close friends is dead or "no longer there" (strokes). Most were health conscious people and the deaths were all unexpected. Joe died in a OV-1 Mohawk crash as he was out by pulling too many G's, Bob a motorcycle crash due to heart probs (he had been passing out), Phil and Cam massive strokes, Dan a Piper Aerostar crash, Barrett and Jack had heart attacks, and more. The one healthy guy remaining is no longer a close friend, as he turned hard core commie.
I've not really been able to make new close friends, but at this point, it does not matter all that much to me. At some point I made peace with it all and am thankful for what I do have!