Honestly, there's a few things to be said about this kind of thing. First off, I never really bought into the "open relationship" thing as it's basically an overglorified "fuckbuddy" to me, someone you can fall back on as you experiment or look for someone you like better. It's a comfort zone thing.

The next is about honest relationships. Jokingly pursuing or admiring other women doesn't exactly mean that they're liable to be unfaithful. Some people don't really believe in the overly advertised "Romantic Love", and may desire other people in addition to their partner. What shows you that they love you is their refraining from doing so.