The repeated image

"Have we met before?" That is what John always says, no matter the circumstances of their meeting.
Sherlock always says no until, one day, he doesn't.
Yes, he says this time. Yes, and there's something I need to tell you. Yes, and I know already that I adore you; in fact, I don't just know it, I feel it.
This is where we always start. This is my twelfth time.

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Or: Sherlock is reborn into the same life every time he dies, and he finds John in them all