Bear in mind that male "gay" relationships are never strictly monogamous, though as a friendship and living arrangement may be truly long-term. Living together, sharing expenses, cruising together. You get the picture.
Female "gay" relationships, on the other hand, are often strictly monogamous. Lesbianism isn't the female equivalent of being a "gay" man, whatever the political alliance. Women aren't men, and if aberrational are still different.
Covenant of marriage is no man-made law, nor is sacrament, nor is ketubah, nor is whatever you want to call it. It is from God and exists without government or for that matter organized religion. It is by definition between a man and a woman.
Civil marriage is the government thing. It is whatever the government wants to call it.
We will have a civil institution of "gay" marriage, not forever but for a while. It will happen soon, whoever is president. Accept this as a fact, but don't stop fighting.
Not sure what you mean by natural law.