Since it's difficult even to imagine why *banning* same-sex marriage would result in a rise in divorce rates, or why allowing it would result in a decrease, it seems that the safest tentative conclusion is that there is no statistically significant causal connection between gay marriage and heterosexual divorce.

In less precise, everyday terms: there's no rational reason to believe that marriage equality has any significant effect on anybody else's likelihood of divorce.

Gay marriage, yes or no, is not responsible for either set of figures. They result from other factors.