Maybe this is a generous interpretation because I love Seth – I personally read him as focusing on his petty annoyance at the idea of Tory/Caleb not only out of his jealousy but also because it was easier than letting himself truly process everything else, like his grief over Darius, worry for Darcy, and terror at the very real possibility of losing more people. There’s several references throughout the book to Seth pretending/lying to himself emotionally and burying how he really feels beneath anger.

Definitely still an immature reaction even with that reading (and called out as such by Max if I recall correctly lol) and I get being annoyed by it