At some point in their lives, almost half of adults in the United States have lived with a partner in a romantic relationship without being married. A 2012 study in revealed that one in 15 couples were in live-in relationships. The legal ramifications of not having a legal marriage are a growing part of family law.
One of the bigger issues is home ownership. The house belongs to whoever is on the deed. It doesn't matter who makes the payments. The equity belongs to the owner of record. Therefore, it is best to buy the house and put in both names with rights of survivorship so it passes to the other partner in the event of death. Another important thing to consider is a will. Without one a surviving partner is entitled to nothing. Unmarried couples with assets of over $5 million needs to be careful of estate tax issues that don't apply to married couples.