Maybe related... or not.

Was listening for something in Chapter 27 and got to the point in 27-2 (around the 12:50 mark) where CJ is recounting what happened in Dunbar the day Kalani arrived. She and Sean were talking:
Sean: Come here.
CJ: Now's not the time. There's too much work to be done.
Sean: You keep doing this, you're gonna break down again. I'm just worried about you.

Kalani got to Dunbar the same day he landed at LAX and CJ says he showed up a couple of days before they were overrun. The timeline puts that a few weeks after Z-day in LA.

So Sean has known CJ long enough to develop a deeper relationship than we see her have with anyone else. AND he's seen her have some sort of breakdown. This could have all occurred between Z-day and Kalani's arrival but I think we're supposed to infer that Sean and CJ go back before Z-day....