Honestly I feel like this is the problem with people trying to keep secrets, in terms of what happened with your sister. I knew I was adopted from a very young age, and every now and then someone at school would learn this and then try and tease me about it, because they thought it should be a shameful thing... But to me it was much more like your childhood sense of this - yeah, I'm being brought up by these people who are my parents now, so what? So the teasing never took because it had no sting in it. At the same time I knew someone who found out she was adopted in the course of an argument with her mum, aged 14 or so, and it blew up her world. (IIRC she was actually the child of someone in the extended family, who'd been too young and unmarried to keep the kid.) It was weird trying to talk to this girl about it because it was the same thing, but how we felt about it was so different. But it was the lies that made it feel so different, not the thing itself.

Absolutely feel you on the five years thing :D I had some FB memories come up the other day of January 2020, just before events took a significant turn...