Two straight men can get married. Unless you are arguing she would perform services for such a wedding the discrimination is not on the basis of sexual orientation.
"People having a same-sex wedding" are not a protected group.
Black people and white people could get married, they just couldn't get married to each other. Therefore when the state prohibited interracial marriage it was not discriminating based on race, it was just prohibiting an activity. "People having an interracial marriage" are not a protected group.
Your legal argument would be laughed out of court.