So you finish a book.
Sure there's the fireworks and crowds of well wishers pounding at your door all hours of the night, but when that fades you are left alone again in your mind. Characters that had moved in and taken space have left.
Possibly you killed them and they shant return. Others found their denouement and have no need to ever see you again, lost wholly to their happy ends.
And you alone in your mind.
Some writers are rather loose and will shack up with the next promising protagonist that happens by. Indeed, I know some writers who have hordes of amorous heroes and heroines clamoring to be the next conquest.
Other writers bid adieu to a story and are more like the widow returning to an empty home after throwing a last flower on a casket set to be lowered. A lifetime with a soulmate is over and recreating that same magic will take time.
I am more like the latter. Sometimes I wish I was a little more strumpet-like.