Does it say anywhere in the Bible that two people have to get married?
There are several references. Here are just a few: Genesis 2:24
For this reason a man will leave his father and mother and be
united to his wife, and they will become one flesh. Matthew 19:5
and said, 'For this reason a man will leave his father and mother
and be united to his wife, and the two will become one flesh'
Matthew 19:6 So they are no longer two, but one. Therefore what God
has joined together, let man not separate. Mark 10:8 and the two
will become one flesh.'[a] So they are no longer two, but one.
1Corinthians 6:16 Do you not know that he who unites himself with a
prostitute is one with her in body? For it is said, "The two will
become one flesh. Ephesians 5:31 For this reason a man will leave
his father and mother and be united to his wife, and the two will
become one flesh. First phrase: When a man and a woman get married,
they are to form a separate family unit. The man is to leave his
father and mother and be joined to his wife. A new family is to be
formed that is distinct from either of the families the two came
from. By the way, the man is not told to join to his wife's family
but to join his wife. I do not think this verse teaches against
ever having living arrangements in the same house. This is much
more common in some cultures than in others. Many times, it is a
financial necessity. However, some form of separation must be made
and a separate place to live is probably the best arrangement. When
the in-laws are too much a part of the new marriage, they often
weaken the new family and the new relationship that is to form.
Second phrase: These two, husband and wife, become one flesh.
1Corinthians 6:16 teaches us that adultery breaks this union of one
flesh. Therefore, the Bible is referring to the physical union of
husband and wife in marriage. Neither the wife or the husband is to
have full mastery over their own bodies because they are now one.
1Corinthians 7:4 states, "The wife's body does not belong to her
alone but also to her husband. In the same way, the husband's body
does not belong to him alone but also to his wife" They are no
longer simply two different people with two different bodies. They
belong to each other in a very literal way.