common-law husband
noun /ˌkɒmən lɔː ˈhʌzbənd/
  /ˌkɑːmən lɔː ˈhʌzbənd/
 - a man that a person has lived with for a long time and who is recognized (in some countries though not the UK) as a husband, without a formal marriage ceremony- She lives with her common-law husband and their three children.