Novel reader here
SPOILER ALERT!!!
There are scenes in the novel that indicate that Kishiar was indeed jealous of anyone near Yuder but it is more subtle and lowkey. There were scenes where he was slightly jealous of good looking men around Yuder specifically Gakane and Enon, and at one point he became jealous when a handsome prince from the neighboring kingdom, Prince Ejain, is showing interest in Yuder like asking him tons of questions about awakening, getting too close to him and asking for his company. It is because of these actions that Kishiar has to put himself in between them.
However, there is less of jealousy moments and more of devotion, genuine love, sexual, trust, and protection betweem Yuder and Kishiar. Trust me, they are so lovey dovey in the novel.

Idc about smut is there a Kishiar jealousy scene?? I'm up to date on the manhwa btw I'm asking the novel readers lol