You're forgetting Yahwi's pov. They met as kids, he was marked by him and keep dating people who looked like jooin, he was hurt at jooin not remembering him and acted like a prick (I'm not justifying him btw) but it didn't matter how many fallouts they had, they always got involved with eachother again
Meanwhile Cain was a complete stranger who says they loved eachother in another life that jooin has no idea abt
Tbh for me it was rlly obvious they were gonna be endgame by the way they interacted in the beginning
It's not that I'm forgetting Yahwi's pov but rather focusing on Jooin's. Yeah, we had that childhood trope but as you mentioned, Jooin didn't really remember that time period and like what I've said, I just feel like there's not enough "deep" foundation for Jooin's feelings for him to be that deadset on being with Yahwi despite everything, with his introspection when they "broke up" and all that talk about self worth etcera even if they always end up on each other's path. Although Cain's appearance was indeed out of the blue, he proved himself to be a good person and he didn't really act all shitty when Jooin didn't remember a single thing from that "past life" stuff. It was also confusing because it really seemed like Jooin gave him some hopes only for him to end up that way. Either way, I'll be able to accept this. I just need more details on their relationship development and a very clear and remarkable change rather than the usual cliche that we have rn.
I still can't wrap my head around this. It's hard for me to accept the endgame because the development is missing. I can't grasp the source of this deadset "love" of Jooin for Yahwi because as far as I can remember, he started having a crush on him because he looks good. It's that shallow so for him to be suddenly deadlocked on being with Yahwi, accepting that maybe he was indeed his fate while dismissing Cain's claims of similar fate, disregarding the pain and all the things that he went through because of Yahwi, it seems like the narrative was just forced to be glued after one another.