From chapter 8 of Possibly I Like The Thrill:
“That’s surprisingly thoughtful of you.”
John gives Sherlock an ‘are you fucking kidding me’ look.
“Well I’m trying to be now,” he admits, knowing historically he’s rarely been what anyone would consider thoughtful.
“I know. And I appreciate it.”
“But you don’t think it will last.”
“I think you’ll try to make it last, but I’m not under any sort of illusions regarding your nature, Sherlock. I know you’ll get caught up in cases and forget I exist, and leave messes everywhere, and forget to pick up the milk, and say insensitive things. Just like I know I’ll storm off and not talk to you when I’m angry some days, and I’ll come home exhausted from work and snap at you when you want me to run off after some criminal. We’re still us, is all I’m saying.”
Sherlock wishes he could deny it, but he knows it’s true. “But we’ll be okay.”