There isn't an advantage that outweighs all the disadvantages. See an attorney before you begin a long term relationship, and stay out of states that recognize common law marriage. Full disclosure: I have been married and divorced. I am now in a long term relationship. We each maintain a separate home in two adjoining states. She is included in my will, but will not be inheriting property that has been in my family for four generations. That will go to my children.