After everything they've been through together, what I can be pretty certain is the end of Kevin and Nora is without a doubt the most miserable moment in the entire series. They were the beacon of light in this depressing series about the aftereffects of tragedy. Now, that beacon of light is gone. And while it climaxed in the final few minutes of this episode, the signs were there all along that it couldn't last. They were both looking to escape. This was inevitably going to happen at some point. This episode especially gave the distinct vibe that they were drifting away from each other. And the fact that Nora so desperately wanted to escape to see her children again, despite the fact that it would mean never seeing Kevin again, made it even more clear that their hearts weren't in each other. Still, that didn't make the breakup any less shocking. This show has always been depressing, but never has it felt so hopeless as it does now.
While the breakup was the main event, there's plenty else to digest. The scientific way to see the loved ones again is a scam. Now the man who set himself on fire the previous episode makes sense, even though he gave a different answer to Nora. It doesn't matter what answer you give, they'll turn you away either way because the transporter doesn't exist. It's just a callous way to build your hopes up, then dash them in an instant. Worse, it instills a sense of guilt that it's your fault they denied the service because you gave the immoral response.
Meanwhile, Kevin's seeing things. Again. His hallucinations haven't gone away. You can pretend problems aren't there anymore but that won't make them go away.
Speaking of, I think that's the real reason why Kevin and Nora's love couldn't last. They had these problems but they never talked about them, as Kevin points out too late. They don't trust each other or love each other enough to help each other through their problems, forcing each other to go through them alone. Patti was right after all. And that's why their relationship didn't work out in the end.