Didn't that happen tho? I remember briefly but yeon gave a soda to a girl in his class as an apology (don't remember as to why) but then a red string appeared and disappeared just as quickly with the both of them. Not sure why it hasn't been addressed since but hopefully it doesn't end up too badly
I think it is because if Yeon hadn't force fate then he would've been with that girl. This is a bl with a happy ending, so it be something like,"the bright Kihoon loved Yeon so much that he wanted him as his fated one. The red stone, pitying the sunshine, gave him one last miracle which combined Yeon to Kihoon.
like i deff love them in historical i just want to see what's gonna happen to them in modern and if anything is gonna come back to bite them in the ass (i doubt it but i think it'd be funny if either of them were to have an alt soulmate and some misunderstandings and wtv happen)