I think this reasoning is flawed. The distance between the two particles is not only the relationship between the particles. The particles itself define a relationship with respect to the distance. Not only does the distance define the particles, the particles define the distance. What you are effectively trying to postulate is that sets of two items cannot exist. The premise that there are two particles implies that there exists some kind of distance, otherwise there would be only one particle.
Another problem with these 'systems', is that I don't define exactly what constitutes a relationship. I am working on a follow-up essay where instead of relationships, these characteristics are defined only in terms of interaction; In this, relationship is past and possible future interaction. It's not an easy thing to do however, and I decided to start in the most clear and concise manner I could. That said, your point is the one that has been raised most to me, and I think I am going to have to draft this introduction again where I address the nature of particles to some degree. Thanks, I appreciate the feedback.