In 1868 with the ratification of the 14th amendment (specifically the Equal Protection Clause). It doesn't specifically guarantee that everyone has the right to

In 1868 with the ratification of the 14th amendment (specifically the Equal Protection Clause). It doesn't specifically guarantee that everyone has the right to get married to anyone that they want, just that everyone must have an equal right to marry anyone that anyone else does. So a state could get rid of marriage altogether, but if it allows it at all it must allow everyone the same choices of who to marry that it allows anyone else.