Yeah... I'm pretty much convinced they can't actually do it until Nasa is able to do something about Tsukasa's immortality. It really would be untenable. But they're being adorably innocent and getting gradually more forward with time, so it's not like we're in any particular rush. And the moment the problem is properly revealed, things will probably get more serious. So let's savor the fluff for now, shall we?
Also reminder that they've only been spending time with each other for about a month, at this point. They're still so very unfamiliar with each other, but the married state is helping them accelerate that familiarity rate.