My GF of just over a year and a half are talking about having a threesome with her other (M) partner. I met him once at a planned public venue and he seems like a great guy. She also speaks highly of him and I generally have a lot of compersion for her and them.

We're all 40-something and have other partners. We're also all straight and we don't expect anything but incidental contact between he and I, so she'll be the focus. We also all practice BDSM, he and I are both Dominant (I'm caregiver leaning, he seems more sadist leaning) and she's more submissive/bratty.

I'm wondering if anyone has advice for our group play time, or relevant experiences that might help ensure we have the needed conversations and shared expectations.