What I have found helpful, is creating a concrete experience of uniqueness. Not only as something we talk about, but something we do. So that each partner not only knows he/she is unique in an abstract way, but also concretely: This is our activity, this is our place, this is our game. This may seem illusionary to some, but I find it is real, totally real, and more important than one might imagine. And something to be respected.
Wow. That's perceptive and wise. You're creating an experience-space that belongs uniquely to those two particular partners. That's not an illusion, it's a really intelligent use of real-world psychology.
I've read sometimes that a partner says, OK you can make love with your other partner...but NEVER in our bed.
Now, really, what does it matter? It's just a piece of furniture, and bedding washes clean. But the reality is it DOES matter and it matters a lot.
It's similar: the importance is psychological and very, very real on that level.
I'm going to print this part of the conversation out for my GF. She'll find it really interesting, being as she is a bit of a relationship-artist.