It keeps him up at night.
Not immediately.
It starts after they get Pike back. Once things have "calmed down", or as much as they possibly can with Jim Kirk in charge… or really, on board at all.
It starts in the aftermath when the ship is in for repairs and the bureaucrats are accosting the crew relentlessly.
In these moments, which aren't as infrequent as he'd like to believe, it really is all he can do to remind himself to breath. Not to panic because she's still here.
In these moments he relives the flashes of death and destruction he received from the few telepaths still alive when the Enterprise had arrived, flashes of fear and desperation.
But she's here with him. He can feel her in his arms. She's warm, and soft, and her continuous heartbeat is more reassuring than he could have ever imagined. He can hear her quiet breaths, peacefully rhythmic. He can feel the steady rise and fall of her chest against his side. He knows she's here, with him.
But he still lies awake at night.
And he thinks… I almost put her on the Farragut.