So all those who can have sex, but choose not to, aren't really in adult relationships? (I'll have to tell my girlfriend that we're both kids.

At least since it applies to both of us, no pedo.) What about those who aren't able to have sex -- say, where one spouse is completely paralyzed. Are they unable to have adult relationships? I'd say no, and I bet you do too. Sex is
usually part of long-term adult romantic relationships, but they aren't necessarily part of it.
And besides -- again, I'm not making an argument that such relationships shouldn't be legally allowed. I'm talking about the morality involved, specifically from a Christian point of view. And I'm hard pressed, as a Christian, to believe that God couldn't possibly ask certain people to not have sex, or not have the sex that they want -- if He could ask us to be willing to die for Him, why not give up sex? You don't have to agree, but I think it's a pretty coherent viewpoint to hold. (And not particularly bigoted. Although we might just have to define that word...)