When the rest of the world became too much for the two of them, when real life reared its ugly head, the one thing John and Sherlock could always count on was that each one knew exactly what to do for the other when he needed a good cry.
Sherlock deduced early on that when John was crying, the best thing anyone could do for him was pretend they didn't see it. He never said so, but Sherlock knew John had been raised in a household and trained in an army where men did not cry, not unless they were spineless sissies. The most sure way to know if John was on the verge of tears was if he tried to hide his face, either by keeping his back to Sherlock or burying his face in a pillow. Sherlock had assured him many times that it was okay, he didn't need to be ashamed, Sherlock would never think any less of him for expressing his emotions, but John either didn't believe it or didn't care. He hid his tears and fought a heartbreaking battle to regain control of himself as quickly as possible.
After a few years of marriage, Sherlock had gotten the practice of comforting John Watson's cries down to a science. As soon as John began to start up, Sherlock would put his arms around him, draw him close to his chest, and not speak one word until John was finished. His husband hated the cliché "It's all rights" and "There, there" and he hated being shushed. With John, it was always better to wait to talk until after he was finished.
He also didn't like having his hair stroked, so instead Sherlock would run his hand up and down his back, slowly. John would press his face into Sherlock's shirt to muffle the cries and ball up the material—or the sheets if they were on the bed—into fists. Crying always made John angry with himself, and Sherlock would try to soothe it by leaving kisses on his head, neck, shoulders, and forehead. Afterwards, John sometimes started to fall asleep, and Sherlock would wrap them both up in a blanket and stay there until John had woken up again and was feeling better. He'd change into a fresh shirt as quickly as possible, so John wouldn't have to be reminded of what he'd done.
If there was one thing John knew about Sherlock Holmes, it was that when the man was shedding tears, the only thing that could make him feel better was hugs and more hugs. John could spot a sobbing fit whenever Sherlock wrapped his coat or dressing gown or blanket tighter around him, like he was trying to give himself the comforting embrace he needed. It broke John's heart, and he never wasted any time pulling his love right into his arms and holding him protectively. Unlike himself, Sherlock did enjoy having his hair stroked, so John would cuddle him close with his arms and pet Sherlock's curls with his fingers. If the sobbing sounded particularly choked, the doctor in him would come out and remind Sherlock to breathe, just breathe, he'd be okay. He would then keep hugging him, saying, "I've got you, you're all right," in a low, gentle voice.
If the crying had to do with John—and it usually did—Sherlock would sometimes throw his arms around John and cling to him like he was leaving forever. In this case, John would reassure him that he was here, he wasn't going anywhere, and he loved him, he loved him, he loved him, between kisses. Sherlock would snuggle even closer to John and cling to him and John was always careful to be the last one to pull away, just to reinforce that he would never, ever leave.
When both of them cried, it was really a mess. Each would be trying to hold the other while still fighting off his own fit, getting each other wet with tears. They would lie in bed in a tangle of limbs and nearly crush each other in tight hugs. Every once in a while one of them, usually John, would try to speak, but find it too much of an effort. When they could breathe again, they would kiss, reassuringly at first and then passionately, each wiping the other's tears away.
Eventually, Sherlock and John would calm down again, and though their eyes would be rimmed red and their hair would be all over the place, they were smiling. Smiling and holding hands as they slipped into sleep.