It's interesting to note that neither society - even in their wildest orgies - ever appeared to have entertained the notion of homosexual marriage, knowing full well, IMHO, that such an aberrant practice would have shortly wrecked their entire societies.
The roman concept was more of domination, not homosexuality as we know it today. As for the Greeks there is a very good reason Greek civilization never went very far dispite everything they discovered and did. It was others that used it to take over much of the world.