Never said love equals procreation, but it is a vital and necessary part to properly raise a child to fit in with society.
As we've been over, and as you've agreed, "procreation" is more than simply impregnating another human being.
The obligations upon procreation extend further than just birthing a new member of our species, yes, but the main goal of procreation
is the generation of a new member of our species, and you'd be unreasonable to deny that. You're losing sight of the primary objective of procreation in an attempt to somehow bridge over the term "procreation" as something that a same-sex couple "could" "do" or "participate in" when by its very principle such a feat would be impossible.
Gay couples can also still impregnate and become pregnant, as I've also demonstrated (though, not by each other, at least not quite yet*...). So even ignoring the definition of marriage as ONLY ensuring the next generation exists survives, ensuring the next generation is something gay couples, and gay married couples, can partake in.
Exactly, a same-sex couple cannot, in principle, procreate. Hence marriage cannot be something that can be extended to them any more than the right to be recognized as a lizard can be granted to another human, any more than the law of gravity can be repealed.
*Scientists have made sperm and I believe egg cells from stem cells - meaning, two gay women could have an offspring that is genetically theirs, and two gay men could have an offspring that is genetically theirs. Under such a scenario, this means that hypothetically gay couples will now be able to fully achieve what you consider to be a "natural law" marriage, be it through unnatural means. Assuming this, would you still oppose gay marriage? I'm assuming you'd protest the procedure through which gay's could have children?
"Whatever, dude," as the kids say. This does nothing to change the definition of a same-sex couple, who,
in principle, cannot procreate. It would be as analogous and as absurd as to saying "Well, a lesbian in a same-sex couple could go get pregnant through natural heterosexual means and come back to her same-sex partner and then 'marry' her, right?" Wrong. That would do nothing to change the understanding of same-sex couples in principle.