Didn’t Cain already explain it to Jooin though? That Jooin was his master in a former life? As far as I remember (I’m too lazy to go back and check) he already brought up the topic.
Yes, but it's not like he accepted it wholeheartedly. If I remember, he just let it go 'cause Cain was persistent. And if Cain would use that as his reason for squeezing himself into Jooin's life, then it may sound unrealistic to Jooin.
I mean tbh I think it’s some kind of messed up loyalty that Cain interprets as love either ways. Maybe it would have worked out under different circumstances but the way things played out it’s just gonna be toxic. They would never be equals in the relationship. I hope they’re not endgame. I hope Cain moves on and find someone he can have a healthy relationship with, both for his and Jooins sake.
I think Jooin will end up picking Yahwi. Everything's just so complicated. If Jooin asked Cain and Cain told him everything, from his memories of being a dog in his past life to Jooin as his past owner, Jooin would not believe it and would only make things more confusing. Like, come on, who would believe that? Cain's character is likable; we all know that, but his background is not just that believable considering the genre of this manhwa. Yahwi's development (?) is plausible and more rooted in reality. And because of that, he is more likely to be picked by Jooin.
Unless the author creates twists of events and squeezes whatever logic they want to insert into the plot.