Starting from personal experience I’d say no. My parents “officially” divorced after six years. My dad has had one girlfreind for six years, and they’re still going strong.
The average American marriage lasts for eight years. The average serious (marriage like) homosexual relationship lasts seven years.
So why is a piece of paper nessacary? If you choose to live with someone for life, why must you apply for a certificate? According to the Christain Bible (which western law is based on), a person becomes “one flesh” after sex. This one flesh can be viewed as a marriage. If you stay with that person for life, than why can’t govement, society, and religion recognize it as a marriage?