He is super worried about him and also has like and overabundance of affection for him because he's been getting a lot of adorable childhood memories lately. And those tend to make him feel guilty because holy shit did he ruin everything or what, but also they fill him with lots of affection and generally make him more prone to fussing over Sasuke even on good days. So the fact that Sasuke has been having a lot of bad days lately means Itachi is extra fussy.

Also Sasuke's reaction to that memory actually kind of scared Itachi, in a way, or at least filled him with anxiety because he's honestly at a bit of a loss of how to navigate Sasuke's new levels of self-hatred. From what he can tell at this point, Sasuke more or less refuses to let himself be comforted and Itachi ends up feeling shut out in spite of being needed because Sasuke can't articulate how he feels. So they both end up frustrated and upset and Itachi gets angry at himself for failing at his brother and blames himself for the communication failure. FEELINGS ARE HARD.

What frustrates Lightning the most about Aather so far?