Thanks for asking a question on www.thisisyourbible.com.
The Bible talks about a man and a woman living together as man and wife but not very much about the marriage ceremony. This couple are truly married in the eyes of God. It is important to our Christian witness that such a relationship be formalized and officially recognized in the community but it is not an absolute necessity. One cannot escape one's marital responsibilities just because one has not officially registered the relationship with the state nor had a ceremony to bless the union. Indeed, a couple in this relationship are considered, for all legal purposes, to be married under "common law."
Here is information available on the website which will help you to answer your question:
Marriage in the Lord: www.thisisyourbible.com/library/show/241
I hope you have found this helpful.