late-breaking gay
n. A person who realizes he or she is gay relatively late in life.
Examples
2010
Some people turn gay late in life. Witness former New Jersey governor Jim McGreevey, who was married twice and had children before he announced that he was a "gay American." Former Clinton pollster Mark Penn even coined a term who out themselves or discover they are gay in their 30s or 40s: late-breaking gays.
—Mark Stricherz, “Sorry, Kagan might be gay,” The Catholic Pol, May 12, 2010
2009
Of increasing frequency are the "late-breaking gays" who abandon their spouse and children for a gay partner. It is depicted in films, in Broadway plays, and on the Oprah Winfrey show.
—Ralph Slovenko, Psychiatry in Law / Law in Psychiatry, Routledge, March 03, 2009
2007 (earliest)
Such Late-Breaking Gays are a growing force in America. While exact numbers are hard to come by, experts estimate that there are at least 2 million gays and lesbians who were once married to people of the opposite sex or still are.
—Mark Penn, Microtrends, Twelve, September 05, 2007