get together vs shack up

get together

verb
  • To start dating; to start being a couple. 

  • to agree 

  • to accumulate, to gather 

  • to meet, to gather together, to congregate 

  • Used other than figuratively or idiomatically: see get, together. 

shack up

verb
  • To live together, especially of an unmarried couple. 

How often have the words get together and shack up occurred in a corpus of books? (source: Google Ngram Viewer )