According to Thomas Aquinas, there are two purposes for sex: 1.) procreation, 2.) strengthening the union of marriage, and 3.) pleasure.
Since procreation can't happen, gay sex is a sin against natural law. If his church allows gay marriage, it still does not satisfy any natural law as set by any diety, even if you happen to be a druid or something like that. If you can't procreate, it can't sustain the species so it cannot be an intent of God.
What if the whole world was gay?
I don't think all gays are going to hell, they should be welcome in a church, but their actions should not be sanctioned.
Churches are full of sinners and AA meeting are full of addicts. I've been to both.