Thinking about while Inej is at sea, gone for months at a time, how Kaz would feel her absence. How he'd come to rely on her, to be used to her presence. And now it's gone. She was like an anchor to him, the only thing that kept him sane those first moments in the Ice Court was the memory of her voice. And just knowing where she was would ease his mind I think, whether or not he was aware of it.
He has no idea where she is, if she's okay. They probably send letters, but that takes time, and anything could happen. She could send a letter saying all the wonderful things she's accomplished and be dead moments later. And he might never know; if the ocean swallowed the Wraith without a single trace ... He would never know how it happened, or if she's still alive and captured somewhere, if she needs him.
And maybe she spends so much time at sea that they drift apart, maybe the letters become less and less, her visits to Ketterdam for shorter times. Maybe years pass and they've missed too much of each other's lives ... Maybe their love isn't enough anymore. It's still there, it always will be, but their lives no longer fit together. Like two islands once so close they almost touched, but as the water and the earth shifted around them they drift farther and farther apart; though still they'd have a piece of each other, the sand from one island washed over to the other and stayed, a seed carried by a bird, an imprint of their time together even as they have moved so far they are beyond sight of each other.
But still Kaz would worry, I think. He would spend those quiet moments in his office wondering where she was, desperately trying to feel the safety of her presence again, grasping for even a glimpse of it like a lifeline. I think he would hate himself for it, for getting attached, for needing her. For spending every spare moment thinking of her, fumbling in the dark of his soul for the tether of hers. I think he'd feel like the frayed ends of a rope, like everything inside him was out of place, like he'd fallen apart without her and been pieced together incorrectly, everything out of place. I think he would go to the harbor to look for her, for even a glimpse of her ship in the distance. Even if they never spoke, even if she never knew he was there, that he saw her, just to know she was there would be enough. To have that tether again.
It would have been mutual I think, they'd have split on as good of terms as two could. They both had the same reasons, not wanting the other to be strung along, the two of them holding two ends of a rope as their lives pulled them farther and farther apart. And rather than waiting for that rope to snap, to fray and split until it was broken, their hands bleeding as the rope burned across their skin ... They let go. Because neither wanted the other to bleed for them, not when both could see that was the only outcome.
And Kaz would want Inej to be happy, to have her life ... To be free. He'd helped her find it, and that was enough. She could never truly be free as long as she was tethered to him, not while her life was at sea, at least. Not while he was still living his same life, the life of the Barrel. She deserved more than that, she deserved to be untethered to a place, or a person, to have her ship and her mission. And I think he would be satisfied as long as she was happy, even if that happiness meant he would never see her again.