Duality is one aspect we can not just shun away easily. It is almost every where. Arabic has even incorporated the fact in their dual noun. Usually we taste the duality just when we are conscious of ourselves. We know that the apparent composed appearance is so vibrated and agitated inside.
Relationships have the same duality aspect. One is the nomenclature of the relationship like mother, daughter, son, father, friend, partner etc. Other is the actual human being to whom one applies the relationship. I like to give an example of a box (the relation) and then you can put a person in that box. The box has certain expectations and the person in the box is always trying to fulfil those expectations. The genealogy of expectations is a debate in itself so won't expound in this post.
There is a further distinction in the relations, one are where we are thrown into. These are inside out relations as we are more aware of the box and less of a man. Hence you will hear people claiming that their parents are the best, or worst as matter of fact. Sadly most of the time we never connect to the person inside. These relationships come with perpetual security, you can't untie the knot ever. The other relations are outside in, these are the one where you connect with the person first. These relations do not have perpetuity. The former ones are the one who you are and latter ones are the one who you become.