The venue is beautifully decorated. Flowers scent the air, and the sound of people chattering floats up throughout the whole room. Tasteful yet cheerful shades of yellow adorn the walls.
Sherlock hates yellow.
The ceremony begins. The bridesmaids are each in their own dresses, picked out in shades of lilac and purple(his tie has a phantom itch to it) and then Sherlock is walking with the other men, (is it wrong to be jealous of other friends?) and he turns and sees John. John. John is handsome and proud and brilliantly happy and it isn't because of Sherlock. Mary is not escorted by her father (he died of cancer), and course, is impossibly beautiful in gold ivory lace. She is bright and brilliant and friendly and everything Sherlock cannot be. John turns to look at her and grins, the same way he does when Sherlock remembers to buy milk or makes a particularly incredible deduction. The pastor has started speaking, talking of some silly drivel about love and commitment.
The pastor turns to John and asks, "Do you, John Hamish Watson, take Mary Elizabeth Morstan to be your lawfully wedded wife?"
"I do." John says solemnly, but eyes bright and full of love.
"Do you, Mary Elizabeth Morstan, take John Hamish Watson to be your lawfully wedded husband?"
"I do." she says.
"I do." Sherlock whispers.
John's eyes fill with confusion for a moment- he glances over at Sherlock, not sure of what he just heard. And in that moment, Sherlock desperately wishes for John to turn to Sherlock and realize how Sherlock feels and leave the ceremony, hand in hand and live in Baker Street forever but with rings and love and cases and experiments. But the ceremony continues. John has already turned back to Mary. The pastor has declared them wedded.
It's over.
Sherlock gives his speech, trying to convey to John how much he cares. John only notices the platonic love. Sherlock forgets, momentarily, and solves a wonderful brain-teasing case.
Playing their wedding song is the worst. He watches John and Mary dance with love in their eyes and it hurts. He leaves because now there is no one for him.
The love song of Sherlock Holmes will never be finished.