pussreboots, Five stars: The Masterful Cat Is Depressed Again Today, Volume 3 by Hitsuji Yamada (2020) deals with separation anxiety. Specifically, Saku's going on the biennial company retreat, a trip she skipped when Yukichi was a kitten.
http://pussreboots.com/blog/2023/comments_10/masterful_cat_is_depressed_again_today_3.html