“The Court’s decision is a recognition that we cannot allow our nation to continue to be segregated into separate and decidedly unequal groups: those adults who are free to express their love for one another in marriage and those adults who are not. As the Court’s opinion makes clear, a wide array of rights and privileges flow from civil marriage. Today’s decision is a powerful, and welcome, affirmation that people should not be excluded from such benefits based solely on their sexual orientation.”