Relationship psychologists and sleep experts express the same kind of opinion. Apparently, the back to back position is very popular with newer couples who have been together for less than a year. It shows that they're secure and comfortable with one another, but there is also a novel element to it. We get the impression that the back to back might just be the gateway sleeping position to the independent. And there's nothing wrong with that!
One important thing to acknowledge is that some newness and honeymoon-style sleeping isn't a bad thing. It's a wonderful and exciting time in your relationship that you should make the most of while it lasts. Keep doing that back to back and maybe one day you'll switch to the independent. Or maybe you won't. Just do whatever feels best for you.