First of all i would like to say that there are some error in my statement, cuz of autocorrect, but anyways i think you understood what i meant.
Now coming to the main topic, you're looking at khaol like he's a human. You think that he's just going to move on from his lover? You must've read stories old love stories, like the ancient ones, where the person would go to any limit, now take it that it's a god this time. Now you'll say that you'll now sacrifice someone for your loved one, but again you're comparing a love of some 2-3 years to his love (idk maybe centuries) so there is that difference. And yeah if I'm not wrong river would not have died, only if he hadn't disturbed lari from killing another human, now ofcourse you'll say what he did was right, & i agree but that was what lari wanted.
Well there are many things i want to say but that'll only make this even longer so i suggest you to read the webtoon again from a 3rd person perspective & yeah looking at character & understanding the environment.
Last but not least I'm not saying that what khaol did is right, but people say that they'll never do that for a loved one, is what is illogical to me.
If you read the story you might understand khaol's perspective, i.e. sacrificing someone for your loved one. Even tho you're being bitch but its not cruel, you'll looking at the story from river's pow so ofcourse you'll feel worst but atleast try to understand how the things are going & logical reasoning of the gods & humans.
And yeah you should also realize that khaol is becoming a better day by day.