1. Very little changed as “same gender” relationships have been legalized for almost a generation (and in most states, including ones most Jews live in, well before that). The only changes pertain to economic aspects of such relationships. “Same sex marriage” is against Torah – filing a joint tax return for two people of the same gender who maintain a common household is irrelevants from a halachic perspective.
2. Contrary to propaganda, there are very few “gays.” Almost all people are “straight” (i.e. hetereosexual). A “gay” species would quickly go extinct. The biggest and most perverse changes in western law, especially in terms of the number of people affected, pertained to liberalizing divorce to the point when marriage became nothing more than temporary partnership, and perhaps most importantly, legalizing extra-marital you know what (by repealing the laws against what had been in the statute books as the crimes of adultery and fornication). These changes occured gradually between the mid-19th century and late 20th century, but are well accepted, and probably more devasting, and more objectionable from a Torah perspective.