cohabit vs go to bed

cohabit

verb
  • To live together with someone else, especially in a romantic and sexual relationship but without being married. 

  • To coexist in common environs with. 

go to bed

verb
  • Of a newspaper: to finish being prepared for printing. 

  • To lie down to sleep, put oneself in one's bed. 

How often have the words cohabit and go to bed occurred in a corpus of books? (source: Google Ngram Viewer )