I really don't have the answer to this one - no one among the living does. So, I'll save that for each man, woman and child to figure out after his body is placed into the Earth and his spirit goes afar. To the essence of your question, however, sin itself and how man measures one against the other, I believe you are correct. That to God, sin is sin no matter which one man commits. But I think he's be very disappointed to learn that those who live together as man and woman and not man and wife weren't taking that next step to commitment in the eye's of God alone because I think he's still see that as fornication or adultery despite how "happy" the couple professes to be. I think he'd still see gays as gays no matter what. That said, as mortal man I don't consider it my job to judge. Just as I'll have to answer for my sins when I'm before St. Peter at the Pearly Gates as he reads from the Book of Life determine if I'm worthy of passage into God's Kingdom, so will everyone else including those who live the LGBT lifestyle.
We're all pretty much happy (more or less) doing whatever it is we're doing down on God's green Earth, but at some point at some point judgement will come. I can only hope that when the time comes I've lived a good enough life in God's eyes to be worthy.