The definition of marriage has changed many times prior to the Obergefell ruling and likely will again.
No, the definition of marriage has always been the union of a man and woman. The legal regulatory parameters of marriage has changed. And now it has been established marriage can be whatever we need it to be in order to accommodate our sexual urges. So yes... it's gonna change radically.
So marriage has never been, say, a man and multiple women?
But fine, marriage in the US has always been between men and women. For the past decade or more, that has been changing. States, territories, even native tribes had incorporated same sex marriage before Obergefell. Other nations have also allowed same sex marriages. I do not know of any instance in which same sex marriage has been used as a winning legal argument to grant another previously disallowed union to become a legal marriage. Have you heard of any such instances?
You say it has been established that marriage can be whatever we need it to be to accommodate sexual urges, but that's not based on the actual ruling. That ruling, so far as I am aware, did not mention sexual urges nor use them as the ruling's basis. Any later ruling which might use Obergefell as precedent could have a hard time if it makes claims about Obergefell which aren't there. Obergefell cited equal protection and gender. Did it say anything about accommodating sexual urges? You may think that is the obvious real meaning of the ruling but I have seen no evidence that allowing same sex marriage leads to the various other forms of marriage you have talked about becoming legal. Can you cite a single instance of a state or territory or nation allowing same sex marriage and then using that decision to allow pedophilia? Zoophilia? Necrophilia? Immediate family marriages? How about even polygamy?
There are a number of other nations where same sex marriage is legal. In the Netherlands it has been legal since 2001, and before that they apparently had something like civil unions starting from 1995. Polygamy remains illegal in the Netherlands. I'm going to guess that they also don't allow people to marry animals or corpses, etc.. If you are so certain that permitting same sex marriage will lead to these other forms of marriage getting state recognition, why doesn't it seem to have happened anywhere same sex marriage has become legal?
And- in no country where polygamous marriage is legal- are homosexuals given equal rights- or allowed to marry.
Generally any country which allows polygamous marriage is as bigoted against homosexuals as Boss is.