Protip: If you're using The Bible to justify your opposition to same sex marriage, don't forget to stone to death any woman engaging in premarital sex. And not just your garden-variety stoning, either. You must gather all the people of the town at the doorstep of the woman's father and kill her there.
God is very specific about this (Deuteronomy 22:20).
If you are a man engaging in premarital sex, fear not. God does not condemn you to death. However, if you were engaged in premarital sex, it must logically be with either with a woman who was also engaging in premarital sex (meaning you must now stone her to death, which strikes me as awkward given the intimacy of your relationship) or with a married woman, at which point you and the married woman must both be killed.
So caution is advised.