To add to my typical argument that legal marriage has been essentially meaningless for a number of decades now, consider the following blurb found in an article on the subject:
For most of the 20th century, couples who lived together before marriage had a greater chance of divorce than those who entered directly into marriage. But when the demographer Wendy Manning and her colleagues looked at couples married since 1996, they found that this older association no longer prevailed. For couples married since the mid-1990s, cohabitation before marriage is not associated with an elevated risk of marital dissolution.