"We wouldn't do that, would we, you and me?"
It was more than talking John's former commander out of removing his belt. It was Sherlock trying to convince himself to stay there. Stay there for John and for Mary and for the little Watson in Mary's womb. It would be incredibly cruel, Sherlock figured, to kill himself at John's wedding. And though he would never admit it to anyone (except maybe the skull), Sherlock cared too much for John to do that again. He had seen what his first 'death' had done to John. And that was something that Sherlock Holmes, a man accused of being more machine than human, never wanted to see again.
And so he held on. The reception went off without a hitch, and Sherlock kept a close eye on John and Mary. He didn't want anything to ruin their beautiful, perfect night. He played the waltz he wrote for their first dance as a married couple, watching as they danced and never once betraying the emotions swirling beneath the cold veneer. When the waltz was finished, Sherlock tucked his violin back in its case and slipped the waltz into the envelope, setting it on the stand. He hadn't really needed the sheet music, but maybe it would make a nice gift.
Sherlock stood in the middle of the crowd. All around him, people were laughing and talking and dancing. Everyone was happy, and everyone had someone else with them that night. Sherlock was alone. The weight of that word hit him that night, and he felt that he was a dark spot on John and Mary's otherwise happy night. So what better way to remedy that than to remove himself?
His violin would be safe here, he knew. John would bring it by the flat when he woke up. Sherlock grabbed his coat and scarf, securing the latter around his neck before exiting the reception hall. He slipped his coat on, collar up, and buttoned it as he walked away from the hall. He didn't know what he planned to do that night. He wouldn't kill himself, that much he knew. Not even he could be so cold.