Kevin Spacey on NPR's Fresh Air:

um, look, i think for whatever reason there are people who come together at certain points in their lives who provide something that no one else has ever provided. i imagine a great amount of that is freedom, and a great amount of that is clarity about "i believe in you and i'm better with you than i am on my own"

but i think what's interesting about this type of relationship is that it seems that these are not two people who view their life through the prism of their relationship. these are two people who have very strong lives outside of each other and have their own interests outside of each other and perhaps even their own friends. [...] and that strength, individualism, that ability to be so concrete in their own lives then when they come together they are even stronger. but they are allowed to operate in their own worlds and give each other that kind of freedom.