I can't deny that (straight and) monogamous marital law is simple compared to marital law that allows for (gay and) polyamorous unions. Espcially poly marital law. It seems like you'd need a variety of types of poly unions, types that make varying provisions for how to divide assets (and handle visitation/custody) if the union dissolves, depending on which type of union a particular poly unit chooses. (An add/drop form would probably be a good way to handle it.) But we've passed plenty of laws that are more complicated than that, and it hasn't killed us. Not that I'm a fan of complicated statutes per se, but for the direction relationships and marriages are headed in, marital laws are certain to keep changing, and the added complexity would be for a good cause.