Isn't he dead
The story that he ran away with the lady was probably a lie to cover her taking him away as her captive swan forever. Her engagement with the ML was fake and they'd both agreed it was just pretend, from the very beginning, they were just pretending to be engaged so that they'd have an excuse to keep meeting and keep trying the ritual to summon their swans, without having the lady's family suspect that the reason she hang out so much with a publicly known demon was because she was secretly another demon herself too (she'd been hiding the fact that she was a demon from her family ever since the very day she was born, so as not to be killed by her family, whom she knew hatefully feared demons).
Thanks
But what happened to her boyfriend there's no way he ran away with that woman and why did she give up the engagement all of a sudden it's suspicious