For me it’s happened twice overtly and I suspect once that didn’t become an explicit request. I’m vocally monogamous, I’m not very social, and I’m still kinda young so I feel like those numbers are pretty high. For me I feel like it’s how I present myself and act, which is pretty stereotypically “queer.” Once that gets picked up on by other couples I think they seem more interested.
That’s a good way of putting it! I normally act without regard for perceptions of masculinity or femininity and I feel like that’s appealing for couples looking for a third.