Isn't that what they're trying to show though? They are in a long-term relationship. The physical and verbal cuesin that scene seem to indicate as much. And if you watch the episode Amok Time again you'll see that at no point does Spock say they haven't seen each other since they were children, only that there was a ceremony when they were kids and the one they're attending will finalize the deal.
T'Pring also states that she has no other way to divorce him but through the challenge. (Maybe because his life is now on the line). And she picked the puny human as her champion because she didn't want either Spock or Stonn to die.The likelihood that Kirk would win that fight was pretty low. So it was logical but, I posit, also came from an emotional place.
I'm kind of excited to see what new layers we get to uncover about Vulcan culture, what new tidbits will be added to existing lore. Like maybe Vulcan culture is not homogeneous. Maybe people have a wide variety of opinions and behaviors operating within the basic tenants of Surak's teachings. Maybe there are people who think sex is just another bodily function and why deny it? And others who think (like many of our religions) that physical desire should be denied. We've already seen extremist behaviors in Vulcans from both ends of the logical spectrum. I reckon that, just like humans, most of them fall somewhere in the middle. Just regular guys going to work and then picking up their kids from the learning centers.
Also, they are a lovely, but entirely made-up, people.
I thought they were freaking adorable together.