double date vs love affair

double date

noun
  • A (romantic) date that two couples go on together. 

verb
  • To go on a double date. 

love affair

noun
  • An affair; a usually adulterous relationship between people who are not married to each other. 

  • A feeling of enthusiasm or strong liking for something; a fondness. 

How often have the words double date and love affair occurred in a corpus of books? (source: Google Ngram Viewer )