A milder true story from my relationship [Real, first-timer]

My (34M) fiancee (25F) Christina, while hot, is pretty shy and nerdy, a little socially awkward, and sexually conservative. She's only had two real boyfriends before me, I was the first she ever allowed to not use a condom, etc. She is generally pretty quiet, a bit OCD, and doesn't like being touched by people she doesn't know well.

We recently moved into a nicer condo building and became friends with an older couple on our floor, Jim and his wife Lauren. They're a bit like us but ten years older (so Jim 40s, Lauren maybe my age). Jim is clearly quite successful, they both drive Porsches, and Christina has become decent friends with Lauren.

We had dinner with them and another couple last week, and Christina was really opening up and being friendly with Jim in a way that's very unusual for her. He works in roughly the same industry as her, and she was talking with him at length, laughing at his jokes, letting him casually touch her on the arm. On the way out of the restaurant he briefly put his hand on her hip sort of guiding her out in front of him, and she smiled and didn't react or show any discomfort. If you know her, that's very unusual.

I haven't said anything about it, but added onto that we see Jim in our complex gym sometimes. He's quite fit and works out a lot for his age. Our conversations are basically normal and friendly, he maybe slightly talks down to me re career stuff. He also made some comments about how he and Lauren keep the spark in their marriage going by being open to new things, etc. I think Christina is too naive to pick up on it, but I basically have interpreted his comments as communicating they have an open marriage and maybe even lightly probing / propositioning us.

I've had this kink on and off from a college relationship / cheating situation, but have basically never broached it with Christina, and I haven't been unsatisfied with our generally vanilla sex life. But having this real-life scenario coming up out of nowhere has my head spinning. Six months ago I would have said Christina would absolutely never consider any kind of non-monogamy, but then she and Jim have this uncommon vibe. It's clear he'd love to find a way to fuck her, although I think he and Lauren are still envisioning more of a swinger / swap situation. I'm not particularly attracted to Lauren, though.

What do I do?