I’m certain that the next time Shanks will meet Buggy, they will be true enemies. Oda is intentionally showing us Shanks in the last few chapters as a young innocent kid eating chocolate and staying behind for his friend’s illness.
He isn’t highlighted as someone of importance like young Teach was for example, but clearly, Shanks is far more important than anyone to be sitting with the Gorosei as we’ve seen.
I believe that something happened to Shanks after Roger’s last voyage that turned him to the other side. Look what Buggy tells Shanks in the panel below.