You are correct Ricky. But it is the only sin that people are trying to justify so that they can continue in it. We don't see people marching in parades to honor thieves, or rapists, coveters, adulterers, liars, etc.
God also did not destroy several cities with fire and sulfur because people were lying, coveting, murdering, stealing, etc. But he did destroy Sodom, Gomorrah and the surrounding cities because of the practice of same-sex. Jude has this to say about it:
"In a similar way, Sodom and Gomorrah and the surrounding towns gave themselves up to sexual immorality and perversion. They serve as an example of those who suffer the punishment of eternal fire."
"But you have this in your favor: You hate the practices of the Nicolaitans, which I also hate.
The practices of the Nicolatitan's was willfully eating foods sacrificed to idols and committing sexual immorality, which Jesus said, "I also hate."
Only one of two things can happen if you go to his wedding: Either you will congratulate him and wish him well, which would be supporting and condoning their marriage, or you will be the downer of the party, showing distaste to their marriage, which is no marriage at all and that because God does not recognize it.
The decision is yours of course, but I don't know how you could, in all good conscious, congratulate them and wish them well.