Since glbt people aren't "allowed" to get married technically and there doesn't seem to be any rules, per se, I don't see how it would be necessarily wrong to have sex before "marriage".
Moreover, I think the lack of marriage rights perpetuates the stereotype of the impermanence of our relationships. I tend to look at marriage of any two people as a sacred thing that needs to be taken seriously. It seems that some glbt couples don't really see their relationships as "permanent" so they feel more or less free to come and go as they please. The other side of that coin is that if marriage is so bloody sacred to the straight community, then why is the divorce rate so high and why are these people allowed to do it again and again, when we can't even do it once!
On the religious side-prohibitions against sex before marriage were so culturally based back then when it was more or less imperative that the Hebrews remain pure, I don't know that in today's cultural aspect, sex before marriage is pertinent.
That's my two cents. For whatever it is worth....
If everyone cared and nobody cried, if everyone loved and nobody lied, if everyone shared and swallowed their pride, we'd see the day when nobody died. IF EVERYONE CARED/Nickelback