On June 26, 
2015, the Supreme Court decided in a 5-4 decision that same-sex couples nationwide have a constitutional right to marry.
The full case opinion (Obergefell v. Hodges) is available here, however, the majority opinion was best summed up by Justice Kennedy as follows:
The right to marry is a fundamental right
Sexual orientation discrimination can be described as being treated differently or harassed because of a person’s actual or perceived sexual orientation, which includes gay, lesbian, bisexual, or heterosexual orientation.
Unlike federal laws that protect people from workplace discrimination on the basis of race, national origin, religion, sex, age, and disability, there is no federal law that