Let me help you out with an explanation of all this (forgive the lenght, but it is all important so you know how recent "traditional marriage" really is.)
Religion does not own marriage, in fact marriage in the earliest sense predates all monotheistic religions by a large margin. As such, all monotheistic religions predate what you hear with "traditional marriage" by a large margin.
We have both Anthropological and Archaeological studies to know that the earliest marriages had nothing to do with love, nothing to do with monogamy, and nothing to do with systems of belief. They originated as a means to handle producing "legitimate offspring" for the purposes of handling name recognition, wealth, and land ownership transfer on a generational level. We also know that marriage started out primarily and only among aristocracy and education (which accounted for less than 1% of the population.) Said another way, early marriage's primary purpose was to bind a woman to a man, often multiple women to a man. It served as a social guarantee that a man's children were accounted for and by effect made a woman a man's property. Among the ancient Hebrew cultures (as an example,) aristocratic or wealthy or other prominent men were free to take as many wives as they wished, often married additional women of conquered societies to add to those numbers. We have evidence taught in ancient history classes of men taking multiple wives, while also having prostitutes, even teenage male and female lovers. Their wives stayed home and handled raising the "legitimate kids" as well as tend to local business and/or farming needs. We even know that wives that failed to product offspring were sometimes given back so someone else could marry them or simply take them in producing kids for someone more common where marriage was not a consideration. For just about everyone else marriage was not available, nor was any recording of who's kids were who's.
Fast forward a little post the advent of at least 2 of the 3 main monotheistic religions and marriage was still more about wealth and aristocracy than anything else. The Romans (for example) used marriage for all the above reasons and even added in the creation of diplomatic and commercial ties all among those important. For everyone else who was starting to marry at the common level, it still was not about religion even though Christianity was starting to take shape post all the conflict with Judaism. Even post Christianity being established as the official sole religion in 380 AD, marriage was *still* about anything but religion.
Marriage did not become sacrament until the 16th Century, as something that should be performed by the church. Western ideologies based on social and economic need. And it still was not about love, it had more to do with family decision making on what was best for both the man and woman. Meaning, prominence and history and family ownership *still* had more to do with this than some "blessing" from above. All the literature from the period is filled to the brim with the difference between family obligation for marriage and the many adulterous relationships one would have for love and romance. The higher you were in social class, the more this was accepted... even in some circles expected. It took until late into the Victorian Era for even the concept of "purity" to show up as having any meaning or relevance to marriage or the church.
When you hear people today talk about "traditional marriage," that did not show up... wait for it... until the early 20th Century with the idea of the "nuclear family" (dad, mom subservient to dad, 2.5 kids, a house and a car) not showing up in the 1950s. So, when SSM showed up as the social direction we are going all the social conservative right is talking about with traditional marriage is a set of ideas that is barely old enough to make the history books. Important, yes. So important as to prevent SSM, not even close.
