Good golf buddies are few and far between; not to mention, best men!
Everytime you think of him for the forseeable future, try to recall the best round of golf you had playing with him, and the best round of golf he had playing with you. It’s a bit artificial, but you’ll have a smile on your face, while you try to adjust to life without him.
So sorry to hear. I’ve lost a really good friend so I can relate. Just be glad for all of the great memories you had with him. I always remember my friend when I’m out doing the things we loved to do together. He wouldn’t have wanted it any other way.