I sympathize with her. Those who have been through a divorce have seen what a travesty our legal construct surrounding "legal marriage" really is. I would not want to enter into a contract like that again either.
Fornication is sex between two people who are not married. Since you're talking about staying with her forever, your question is really about whether or not God would consider the two of you married if you did not get legally or officially married. I found a website that discusses this:
https://www.gotquestions.org/marriage-constitutes.html
"The problem here is, what constitutes marriage according to the Bible? The Bible nowhere explicitly states at what point God considers a man and a woman to be married. Due to the Bible’s silence on this matter, identifying the precise moment a man and woman are married in God’s eyes is a complex undertaking. Here are the three most common viewpoints: 1) God only considers a man and a woman married when they are legally married—that is, when they become husband and wife in the eyes of the law. 2) A man and a woman are married in God’s eyes when they have completed some kind of formal wedding ceremony involving covenantal vows. 3) God considers a man and a woman to be married at the moment they engage in sexual intercourse. Let’s look at each of the three views and evaluate the strengths and weaknesses of each:
1) God only considers a man and a woman married when they are legally married. There are some weaknesses and potential problems with this view. First, marriage existed before any government was organized. For thousands of years, people were getting married with no such thing as a marriage license. Second, even today, there are some countries that have no governmental recognition of marriage, and/or no legal requirements for marriage. Third, there are some governments that place unbiblical requirements on a marriage before it is legally recognized. As an example, some countries require weddings to be held in a Catholic church. Fourth, to make the legitimacy of the marriage union solely dependent on government statutes is to indirectly sanction the statutory definition of marriage, which may fluctuate."
