Exactly. My best friend’s husband and I have texted just the two of us. It’s totally innocuous: he’s picking me up from the airport when I’ve visited, or about sports (about which my best friend cares not at all), or maybe a book somebody read and really liked (“Best Friend said you just finished Book, would you recommend it?”), or if he’s with their kids and one of the kids does something cute, he’ll send me a pic or video. I also have a group chat with both of them. But my best friend knows about all this (sometimes I’ll mention it to her during an exchange, in fun, like “your husband is trying to say team x is better than team y; please tell him he’s tripping”). If she wanted to see screen shots, I’d be like “Here you go!” There’s nothing furtive about it. If Zach and Lindsay thought their friendship was so innocent, they’d have mentioned it off top. “Hey, your friend Lindsay DMed me” or “I reached out to Zach” or whatever. I can’t remember who reached out to whom first, but the fact that they kept it a secret is problematic on its own. If it was that innocent there wouldn’t have been all this lying about it.