Live in sin
Definition 1 of 1
Pro Tip 1/3Cultural Sensitivity
This phrase can be considered judgmental or outdated in cultures where cohabitation is normal. 
They were warned that older relatives might view them deciding to live in sin as scandalous.
Pro Tip 2/3Emotional Connotation
'Live in sin' often carries a negative undertone implying moral disapproval. 
Despite the gossip, the couple was content to live in sin.
Pro Tip 3/3Informal Usage
Used in informal contexts, this phrase might not be appropriate for formal or written English. 
When joking, they'd say they're living in sin.