Sherlock, a high functioning sociopath, not understanding the human being, thinking of himself sitting alone for several days may sometimes feel disturbed at being so different. So he needed a roommate to fill his chair across the way. Obviously, he did nothing at random, he took John Watson. They began their inquiries, became good friends. This is why Sherlock feels better, he is alone but accompanied. What is incredible is that Sherlock rarely expresses his feelings, he will be drugged, he will be invaded by his work. But all of this would not be Sherlock, if John did not keep his blog with his adventures but especially by making Sherlock a star, which evidently delighted him. But since he is "the great Sherlock Holmes", "the only detective consultant," etc. Many of his acquaintances regularly worry about him, his sister Eurus wants to play the violin with him, his brother Mycroft will protect him whatever happens, Molly will take care of him and will remind him of his slips so that he remains in the right way , John despite his personal life has a lot of affection toward Sherlock, ect. Here, a certain loneliness because of his way of thinking is largely repaired with his notoriety. Without knowing it, Sherlock will always love this game, hide, play, stop, start again.