My best friend in the sense of the person I love talking to about books, films, clothes, gossip, our children is my sister. We "get" each other, wordlessly. I can tell her things that would probably put me in a bad light if it was anyone else.
Like MrsDevere, I don't have that with my DH.
He is quiet. I talk a lot.
I work, he is a SAHP.
I love traveling, he is a home bird.
He has passions (photography, computers, gardening, football) which leave me cold.
I have passions (reading, MNing, feminism, baking) which leave him cold.
Yet my DH and I have a deep love, huge respect for each other and we like spending time together, going on holiday, going out for dinner. We do talk to each other about everything but our lives are not overlapping.
He is a wonderful husband and I adore him. But he is not everything I need, nor am I everything he needs.