Lets see your evidence. Usually the gays point to their posterboys. Nero and Elagabalus. Nero, deballed his boyfriend, dressed him up to look like his ex wife and married him. Elagabbalus, who whored himself out to men in the Palace, also married his male slave. But, of course,
It should be noted, however, that conubium existed only between a civis Romanus and a civis Romana (that is, between a male Roman citizen and a female Roman citizen), so that a so-called marriage between two Roman males (or with a slave) would have no legal standing in Roman law (apart, presumably, from the arbitrary will of the emperor in the two aforementioned cases).[56] Furthermore, "matrimonium is an institution involving a mother, mater. The idea implicit in the word is that a man takes a woman in marriage, in matrimonium ducere, so that he may have children by her."
http://en.wikipedia.org/wiki/Same-sex_marriage