JohnLock: This Is My...

John and Sherlock were in a fix. It was for a case. Actually, more than one. Where it required for them to be together.
Constantly.
***
"John, come on, we're going to dinner," Sherlock ordered as he wrapped his scarf around his neck.
"Sorry, why?" John asked as he stood up.
"Lestrade's given me a case. Potential murderer. He's been targeting couples." John furrowed his brow.
"What, so you're suggesting we go out on a date so we can be murdered?" Sherlock rolled his eyes.
"Be realistic, John." It was John's turn to roll his eyes as he sighed. No use in arguing with the sociopath.
The two made their way to a fancy restaurant, one that was much too expensive for their budget. Luckily, Sherlock nicked his brother's credit card over his last visit.
"Welcome," a man at the door said. "Good evening, Mr. Holmes." Sherlock nodded.
"Evening, this is my..." Sherlock stumbled to find the right word as he looked at John. "...boyfriend." John closed his eyes in embarrassment and annoyance.
This was going to be a long night.
***
"John, we have another case together," Sherlock stated.
"What, another couples case?" John wondered.
"Here, take this." Sherlock tossed a ring with a single diamond in the band towards John, where it landed expertly in his open hand. He furrowed his brow at the jewelry, then looked at Sherlock.
"What am I supposed to do with this?" he asked as he held up the ring.
"Put it on," Sherlock said, as if it was obvious. "See, look, I already have mine." Sherlock held out his left hand, which held a similar ring on his ring finger.
"Sorry, so this case is about us being fiancees now?"
"Course." John sighed. Here we go again.
***
"Sherlock, where have you been?" John asked, a little bit too harshly than he meant to. Sherlock set his scarf and jacket on a hook as he entered the flat.
"Met up with Lestrade, then had to go out shopping," Sherlock inquired. John raised his eyebrows in surprise.
"You've gone shopping?" he asked, then furrowed his brow. "Where are the bags?" Sherlock gave an annoyed look as he went to sit in his armchair.
"Not that kind of shopping," he corrected. "This." He reached into his pocket and pulled out two faded gold wedding rings, handing one to John. Taking it reluctantly, John looked it over.
"So you went out, met with Lestrade, and then bought wedding rings why?" John asked.
"Last case in the string of couples cases. Last murderer in the cult."
"So this one, he goes after married couples?"
"Yes."
"So you want us to be married?"
"Yes." John looked at him to see if Sherlock would catch on. "Oh, not actually, I wasn't... This is just for a case, strictly professional." John nodded and put the ring on, knowing that he would have to no matter what.
But he would never tell Sherlock how much he loved these cases.
Extended Ending
Lestrade looked over the case file. The fake case file. Oh, how fun it was to trick Sherlock.
"You're never going to tell him, are you?" Donovan asked from the doorway of Lestrade's office. He laughed heartily.
"Never," he stated. "It was about time they got together." He looked at the file fondly, feeling accomplished. "The detective and the doctor. Is it bad that I feel really happy for them?"
Suddenly, a loud yell rang out from behind Donovan.
"LESTRADE!" Sherlock yelled. "WHERE THE HELL ARE YOU?" Lestrade quickly took his feet off the desk and stood up to brace himself for the rant that was about to be unleashed on him. He looked at Donovan with a little grin.
"I regret nothing," he stated.