As I already told you, they are related only in the sense that marriage is involved. But pretty much everything is related if you stand back and squint. Are they related in such a way that the guy in the OP can claim a right to commit bigamy because gay people can get married? Nope. Polygamy is not an argument for gay marriage, and gay marriage is not an argument for polygamy. In fact, considering the low opinion people usually have for polygamy, and the negative connotations, (especially among Mormons, for example) I regard conflating gay marriage with polygamy as not-so-soft homophobia.
Its beyond obvious that one thing can eventually lead to another, so I'm not sure what you're on about. I didn't say, even once, that the gay marriage ruling wasn't going to be an eventual factor in further marriage law reforms. Never even implied it. Its just a straw man. If you can quote me saying that the gay marriage ruling isn't going to be an eventual factor in further marriage law reforms, please do so.
Do I think polygamy is going to be legalized anytime soon? Not a chance. Probably not even within my lifetime. Should it be? Yes, obviously. But now we've wandered way beyond the scope of what I was saying.