“Because Section 3 of the act defines marriage as being between a man and a woman, same-sex couples who are legally married in nine states and the District of Columbia are denied the benefits of more than a thousand federal statutes and programs available to other married couples. Among other things, these couples cannot file their taxes jointly, take unpaid leave to care for a sick or injured spouse or receive equal family health and pension benefits as federal civilian employees. Yet they pay taxes, contribute to their communities and, like all couples, aspire to live in committed, loving relationships, recognized and respected by our laws.