A lot of people sleep alone... or alternatively, have a pet (or two!) and/or a baby co-sleeping!
These days, Mrs. Bee sleeps with Smokey the cat in the nursery, and I sleep in the main bed. Sparky the cat used to sleep with me, but she is no more. It works out that we can both hear our respective bosses (i.e. Charlie and Olive) better this way.
How many mammals sleep in your bed on a regular basis?