This troper and her lifelong best friend grew up spending most of our free time together, but only dating other people. We often introduced each other as brother and sister. When we walked around at our ten-year high school reunion, no one even seemed to REMEMBER that we'd been 'brother/sister' best friends in school, in fact, the first words out of almost everyone were 'Aww, you guys are still together!' Turns out that yes,
everybody but us DID see it, and that reunion was eight years, a wedding, and three children ago.