Author note: I can't really picture these two being lovey-dovey or schmoopy, but they work as a couple to me anyways. Also, yes, Sherlock has a pet name. I'm sure John would insist on one, and that's the only one that seems to fit. John doesn't get one, he's just 'John'. But it's said with love :D
Mycroft Holmes sat like a statue on the sofa of 221B Baker Street staring at the pair of them incredulously. Hell had finally frozen over.
"Oh do close your mouth Mycroft. You look absurd." Sherlock stood with his back to his brother, calmly toying with his violin and occasionally making notations on a few pages of sheet music.
"John, you realize it isn't too late to come to your senses? You could be considered for sainthood simply for living with my brother, much less… this."
Sherlock screeched out an irritating note on his violin, earning a glare from his brother and John. He pretended not to notice.
"Look, we're not asking for your permission-" John started, trying to be the sensible one of the two of them.
"Thank god."
"Sherlock! Not helping."
The screeching resumed. John snatched the bow out of his hands without looking up.
"You'll forgive me if I never expected my brother to have a relationship at all, much less a marriage."
"Yes, well, life is full of surprises." John held the bow further out of Sherlock's reach. "I wasn't expecting it either, but here we are."
"John, is that any way to treat your partner's things?" He wheedled.
"Shut up, Sherlock, you're behaving like a child." John glared at him, clearly not amused.
Mycroft raised an eyebrow, shooting the doctor a meaningful look, which Sherlock fully noticed. He moved to stand behind John's chair in a huff, still keeping his back to his brother. John set the violin bow aside.
"Look, the fact is, we're making this official. I'd like you to be a part of it." Mycroft noted he didn't say 'we'. "You can choose to attend or not, but it's happening either way."
"Not, is preferable."
"Shut up, Sherlock."
"Certainly. I'd be delighted to attend. Let me know if I can assist with any arrangements." Mycroft's tone was clearly intended to gall his brother. It seemed to be working.
"Be sure to leave some cake for the guests, Mycroft."
"Sherlock-"
John turned to glare at him as the door to their flat opened and closed behind the elder Holmes brother.
"Was it really necessary to involve Mycroft of all people?"
"Remind me who kept you hidden while you were 'dead' a few years back?"
"… Alright, fair point."
"And this, love, is why I'm handling the invitations." John patted Sherlock's curly hair as he stood up, handing back the violin bow.