I went back to re-read since i forgot who Stand was!
TLR ----> Re-read chapters25-28 for the history between Leylin, Del and Stand. It's complicated.
So! for anybody else who forgot like me and doesn't want to re-read:
Stand is Leylin's distant cousin from her father's side.
He and Leylin were close friends as kids and Leylin even told him about her past life, but he just took it as a kid's imagination.
Her father publicly announced that Leylin and Stand would be engaged when they were both kids.
Leylin publicly and loudly refused to marry him, since he was family and like her older brother.
Stand actually did love her and was heartbroken. The family also blamed him/became suspicions because Leylin had rejected him so harshly.
He left.
Leylin felt bad afterwards for rejecting Stand so harshly but he was already gone and couldn't apologize.
She hasn't met him since.
Stand however got picked up by the emperor.
He helped the emperor conquer the world(Didn't have much of a choice) and even Sophen, his birthplace.
He's the one who created Del's sedative cigars.
He's also created new administration and laws to manage the new territories.
A lot of this was done by inspiration from Leylin's
'other life' stories which she had told him.
Stand and Del obviously know each other pretty well, including past engagements.
Stand was the one to warn Del that the drugs in his blood could kill Leylin.