
They are in a dom/sub relationship as well as their normal relationship- it’s been like that since the beginning and it’s been very clear that they are sadomaso but also switches as well, if you didn’t catch a hint then get one- This is a good representation of harder bdsm with consent and boundaries, they have a safe word, they consent, get a grip(⊙…⊙ )
For those wondering in the main story those were promise rings, not engagement rings. Beom is actually saying, “be my wife” now as to in the main story he was in a way saying “you’ll be my wife soon enough”.