Thinking back on partners I've lived with... married and otherwise... how good sex can be a kind of inoculent as you get to know one anoth... .... then I think... "know one another?" I don't think so.
What is it then? More like... learning each other's moves. When to cuddle, when to duck, when to offer a hand, or ask for one... when to just stay out of the way. when it didn't work... pretty much what it came down to, aggravating whatever underlying dissatisfactions might be present... if you get in each other's way. Have the wrong moves... no coordination... it won't work.
Has to be a kind of dance, where the movements, the accommodations, the comings together and the retreats--feel right in themselves. Describe something... like a dance (and how many dances describe exactly this?) It's choreography.
No one can hope to "know" another person... the hope is... while hope lasts... that you can learn to like their moves, and they yours, and learn to move together... pas de deux ... of life.