He just can’t quit those games
"You're home early," Sherlock said surprised, "date not go well?" "It didn't go at all," John replied, "I went to pick her up and found her shagging her ex on the sofa with the door wide open." "That's unfortunate," Sherlock winced, "have you eaten? We could go to Angelo's." "That would be great," John smiles. "I'll get my coat," Sherlock says getting up. Dinner goes so well that John stops dating women and starts seeing Sherlock.