It doesn't matter to John that the world has disowned him, that it has discredited and destroyed him, he still believes wholeheartedly. How can he not believe in the wonderful mad genius that is Sherlock Holmes. Society can believe what it wants but John knows the truth. Sherlock was never a fraud and nothing anyone can say will ever change that. John doesn't, can't believe Sherlock's confession for he can't, won't let Moriarty win. Moriarty may have taken Sherlock away from him, but John won't let him take their memories together as well.
John stands proud, of himself and Sherlock despite the lies in the papers and the abuse that falls from idiots lips. He stands alone, faithful to the greatest man John has ever known while the others, the ones who know Sherlock, know the truth about him, slink into the shadows. Let them hide, let them bleed, let them suffer like Sherlock did.
John remains marked by Sherlock and the events leading up to Sherlock's fall. Eventually the initial desire to fight, to hurt anyone and everyone who belittles Sherlock dissipates. John cannot fight everyone after all. The stress wears him down but John never gives up hoping for Sherlock's eventual return. Sherlock isn't dead. He's not the sort of man that can be killed so easily. He's a phantom, a legend, he's alive. John isn't sure how he knows, how every fiber of his being can be so sure when all evidence suggests the opposite but he's sure.
John still writes, the desire to do so is still strong in him after all but John has nothing much to say. The same five words find themselves spilling out across the page. I believe in Sherlock Holmes. John writes them on his blog before abandoning it along with several other websites that say much the same thing. Soon he finds the city replace his paper and a spray can his pen. He starts subtle, but it isn't long before the words or a variation of such are elegantly covering almost every major surface in London. The police of course don't appreciate his handiwork but John has been around Sherlock long enough to avoid being caught.
John knows he should move on and forget about Sherlock forget about their adventures. But he can't delete things from his brain like Sherlock can. Even if he could, he wouldn't want to. His therapist tells him to go out, meet a nice girl settle down and get married. She tells him to go have some kids and live a normal life and get old . He tells her that her plan sounds boring and that he already had a family. He had Sherlock. She tells him he is sabotaging himself and that he will never get better if he doesn't start listening to her. John makes a point of going out and getting pissed just to spite her. He turns up at the next appointment wearing a shirt with a low collar that just about shows of the new tattoo on his neck. Sherlock's initials in swirling dark black font. The letters calm him, bind him to Sherlock. He may never come home, may not be able to but at least there was someone waiting who cared. His therapist doesn't understand when he tells her this, she thinks he's obsessed with a dead man. John pity's her a little for she doesn't get it, he's in love. Completely wholeheartedly in love.