Marriage means one thing, the union of a man and a women in order to create a family.
Marriage is not sharing housing, it's not friendship, and it's not sex. Ideally it includes all of the above, but not always.
Two people of the same sex can't be married to each other, they could be sharing home, be friends and having sex, but they'll never start a family unless a third person from the opposite sex comes in and breeds.
That's it, same sex marriage is not marriage, it doesn't matter what your religious beliefs are (belief in god A, god B, god C, twist on any god, no god). Words have meaning, you can't choose to call chairs and tables the same, they will never be the same thing, the rest of the world will keep their words associated with their meanings, in the end you will be the weird people who call tables "eating chairs" or chairs "sitting tables" because you will need to distinguish between the two things in order to explain (same sex marriage/gay marriage).
Even tho the "west" (which ceased to exist a long time ago, we are just the nwo) calls it marriage, we are a tiny fraction of this world's population, and the rest of the world (central&south america/ africa/ asia/ russia) isn't going along with it.