lover vs sex partner

lover

noun
  • A sexual partner, especially one with whom someone is having an affair. 

  • A person who loves something. 

  • An informal term of address for any friend. 

  • One who loves and cares for another person in a romantic way; a sweetheart, love, soulmate, boyfriend, girlfriend, or spouse. 

sex partner

noun
  • Someone that one has sex with, especially on an informal or casual basis. 

How often have the words lover and sex partner occurred in a corpus of books? (source: Google Ngram Viewer )