Hi, and thanks for your question.
The Bible doesn’t use the phrase ‘living together’, but it does describe living in a sexual relationship outside marriage, the lifelong covenant between a man and a woman, as ‘fornication’. Marriage as a way of living and an institution is found throughout the Bible and is taken for granted when the New Testament speaks of the relationship between a man and a woman. Creation accounts are often referred to, see Genesis 1:27; 2:24.
Other Bible verses relating to this are: Malachi 2:14; Hebrews 13:4; 1 Corinthians 7:2, 9 and 1 Thessalonians 4:3–5.
Best wishes, boyandgirl.info