Marriage laws state by state – in which states are same sex marriages legal and which states have DOMA provisions in their constitutions.
Divorce rates by state, sorted based on availability of same sex marriage.
Public support for same sex marriage, state by state including change in support over time.
These graphs are easier to read, public opinion on same sex marriage, a Federal Marriage Amendment, and anti-discrimination laws broken down by age of respondent.
A useful exchange between Andrew Koppleman and Robert George – these posts and the linked papers should give you a good sense of the contours of the debate over the natural law position on marriage.