Mycroft sat across from Lestrade with a frown creasing his face.
Greg sighed and put down his tea. "Is something wrong?"
"Hmm?"
"You've been…staring at me for the past ten minutes," Greg snapped.
Mycroft shifted slightly and was glad they were in his house and not in a public area. Greg had many good qualities, but his loudness and brutal honesty were not on that list. "I was merely thinking."
"About what?"
"My dear brother."
Greg rolled his eyes. "What's Sherlock done this time?"
Mycroft took a sip of his tea. "Nothing. I was just thinking about his relationship with Dr Watson."
"John? Well they're friends aren't they?" Greg let out a sigh. "Though I never thought I'd see the day that Sherlock Holmes opened up to someone." He shook his head to himself.
Mycroft's frown deepened. "Then you are not aware of the new level that Dr Watson and my brother's relationship has reached."
Greg frowned back at him in confusion, trying to decode the meaning of the statement. "I haven't…what?"
Mycroft leant back on the chair. "My brother is currently sleeping with the good Doctor."
Lestrade spluttered. "What? Since…what? When?"
Mycroft eyed Lestrade. "Approximately two weeks, give or take."
Greg thought about it. "No wonder John's been so happy recently." He shook his head and reached for his tea, lost in thought.
Mycroft watched the reaction with interest. He was still a bit worried about Dr Watson's relationship with Lestrade. He had been unable to find out much about their friendship.
Dr Watson clearly had something more going for him than meets the eye, if he was able to captivate Sherlock's attention. If he was completely honest, he was a bit jealous of Watson's uncomplicated relationship with Greg. Though the idea of 'going out for a beer' seemed to him completely horrendous, he despised the idea of Greg spending time with anyone else.
"You okay?" Greg asked him.
"Yes," Mycroft answered. "Just thinking," he clarified again.
Greg gave him a suspicious look, then shrugged. Ah to be as simple as Greg Lestrade, Mycroft thought. Because he was, really, a honest, unassuming person. He probably wouldn't even suspect other people's designs until it was too late. And that was why Mycroft had to look out for him. Greg couldn't be trusted to look after himself.
"Does this mean we'll be double dating?"
"What?" Mycroft asked confused.
"You know, having double dates….with John and Sherlock."
"Pardon?"
Greg rolled his eyes. "If they're dating, and we're dating, are we going to do double dating?"
Mycroft frowned. "Whatever for?"
Greg gave a laugh. "Because that's what people do!"
Mycroft gave him a cold stare. "I doubt my brother would welcome the intrusion."
Greg rolled his eyes again. "What's gotten into you?"
Mycroft debated whether lying or truthfulness would be most effective. "I think you should no longer seek Dr Watson's companionship."
Lestrade paused, once again trying to decode Mycroft's flowery way of talking. "You…don't want me to see John anymore?" And then he felt a bit bad because that made it seem like John dating him and not Sherlock. And they weren't.
Mycroft too picked up on it. "Yes."
Lestrade frowned. "Why?"
Mycroft looked down into his tea, trying to formulate a proper and foolproof reason why his lover shouldn't see his brother's lover.
Unfortunately, Lestrade, although a simpleton in most areas, could figure out some others. He laughed. "You're jealous!"
Mycroft looked up sharply. "Hardly," he said dryly.
Lestrade stood up, walking around the table to sit next to Mycroft, who shifted uncomfortably with the sudden proximity of his lover.
"Yes you are!"
Mycroft racked his brain to try and find a moment when Greg had looked so excited and happy and evil outside of the bedroom, but failed to recollect one.
Lestrade on the other hand, was ecstatic. So Mycroft had a chink in that seemingly perfect armour then? He immediately made note to see a lot more of John. He gave a goofy grin and leant in for a kiss.
Mycroft didn't resist, but he did mentally curse himself for his lack of tact.
And then Lestrade whispered some suggestive things in his ear and Mycroft decided that perhaps his jealousy wasn't a complete annoyance.

Eck, don't mind me, I'm just writing brief one-shots to get over my Supernatural Season 8 Finale Feels.