No sex is allowed to marry the same-sex. All sexes are under the same restriction. Not all races were under the same restriction. Blacks were only barred from marrying whites, but were still free to marry any other ethnic group. So to were whites allowed to marry any ethnic group other than Blacks.
Gays can marry gays as long as the gay they want to marry meets the criteria.
If a gay chooses a gay who is already married, the government will rightly discriminate against that gay couple.