Witchery

I KNEW IT. The stable, kind, objectively great love interest with zero emotional baggage ALWAYS gets randomly nerfed with secret degeneracy or closet skeletons to make the FL get back with the toxic trainwreck OG ML

This is really interesting because Luhan is essentially written as an undercover nice guy. He became obsessed with her over a single interaction (with one sided emotional significance on his part).
He deliberately waged an elaborate information war to sabotage every other marriage option she had, to the point it became so well known it negatively affected her reputation in society. Even while this was happening throughout an entire decade, he never actually stepped up to put his hat in the ring. He never tried to court her, confess his feelings, or win her over.
His entire game plan is just controlling her environment until he’s the only option, and once he got there he still didn’t try to make an honest attempt to win her over. He came up with a plan to manufacture a trap to allow him to socially blackmail her family to force a marriage with him.
He gets to the altar and surprise, surprise, a marriage certificate doesn’t magically create romantic affection. He doesn’t understand the most basic realities of relationships. He only knows her superficially and objectifies her while trying put on a “husband performance” to secure her affection. He isn’t actually trying to get to know or connect with her, but panics constantly over her lack of interest/commitment.
He thinks the issue is that he needs to do a good job as her husband when the reality is that she just doesn’t know him and isn’t terribly interested in sparking a relationship beyond what is mandated by their marriage itself. He has a very superficial understanding of what actually creates a relationship.
He puts so much effort into limiting her choices and looking “successful”, but doesn’t bother trying to get to know or connect with her, then gets upset that she’s not head over heels for him.
He’s panicking over the potential for divorce and where are the first places his mind goes to prevent it? Physically imprisoning her and using magic to brainwash her, not trying to get to know her more, not going on outings, not actually pursuing a real relationship like he should have from the beginning.
Luhan does not love her, he does not have a crush on her. He wants to possess her and mistakes that desire for love. He has no regard for her opinions, emotions, or autonomy. Almost every single action he has taken or considered taking to secure/solidify this marriage has been at her expense. He has risked nothing of his own, but done plenty of damage to her.
His interference with the suitors was so well known that she became a laughingstock because she was perceived to be so undesirable that literally not a single person in high society would even consider courting her. She had no choice in her marriage to him because he manufactured a situation that would be extremely harmful to her and her family if it got out, so it really was her loss.
He casually considers chaining her up, preventing her from going anywhere without him as well as full on brainwashing her with magic to be loyal/loving to him. Problematic for obvious reasons, but I think really illustrates exactly what he thinks of her. He has said that he admires her strength, competence, and upright actions, but the second she might slip away from him, he’s considering destroying all of that as long as she can stay in his possession. He’s not interested in a genuine connection because if he was, forced confinement and mind control wouldn’t be on the table.
He wants compliance with his fantasy of a relationship more than he wants an actual relationship. The only reason he has largely gotten away with it is that he has ML privileges. In most stories he would be the villain in opposition to the ML.
He is a chillingly realistic, menacing, and manipulative nice guy character. He is not the type to throw a tantrum after not getting his way and this be rendered unable to find a relationship, but rather the kind whose relationship explodes 10 years in after his SO discovers his grievous deceptions and manipulations.