"You're forgetting that there is limited space here," Sherlock pointed out. "We'd have to share rooms with others. If you're alright with the idea of us having an open relationship under the event parameters, then I suppose that would work out fine. One of us can stay here and the other can... well, find alternative companionship."

The very idea made Sherlock's blood boil. John kissing some strange woman, his lips on her flesh marking her like he had him, hands holding her close, rocking into her on the waterbed with Newton's third law adding some benefits to the bed's design. John liking it better. John changing his mind.