Thinking about Rocky watching his crew sleep and waiting for them to wake up, even when they're already dead, because he can't know when they're dead because it appears exactly the same as when they're asleep
Thinking about Rocky watching Grace sleep, and knowing he's alive because of the sounds his body makes during his sleep. His heartbeat, loud enough for Rocky to hear, a reasurring sound that Grace is still alive. Grace's breathing, the rythmic rise and fall of his chest.
Thinking about how Rocky will know when Grace finally dies, because those familiar sounds that were always there the whole time they knew eachother will fade out and go silent.
Thinking about how Rocky might have been more shielded from the radiation than his crew, but still wasn't completely shielded. About how eridians aren't built to deal with radiation. About how Rocky might not live that long after Grace dies after all. About how Rocky might not have to live on very long without Grace, and without Adrian, who will surely be way older than Rocky because of the time expansion, the same way Stratt was older than grace in the epilogue of the movie.