A Romo is a person who engages in a heterosexual relationship to cover up the fact that they are homosexual. Romo can also refer to the deceptive relationship itself.
"Is Mattgay?"
"No, he can't be, he's married"
"Maybe he's a Romo"
"Matt's wife was complaining that they never have sex"
"Yeah, that whole relationship is probably just a Romo"