Party member romances a monster/villain

>party member romances a monster/villain
Has this ever happened in one of your games? How did it play out?

But Elias isn't a villain, he's best husbando

...

No, i'm not a terrible GM

This is back in 2e, but my elf cleric romanced and eventually married a drider. She was a priestess of Kiaransalee who found and took my character as a slave when he was lost and separated from the rest of the party while venturing in the Underdark. She was relatively 'kind' to him, making sure no one else touched him, save herself and, on one occasion, her high priestess, who forced her subordinate to let her bed her "steely-eyed" pet.

He eventually escaped and met up with the rest of the party when a warband lead by a priestess of Lloth — of whom the party was tracking and was the reason they were in the Underdark in the first place — attacked the small temple Kiaransalee.

We eventually found out later that the priestess that had taken my character as a slave was, herself, taken captive by the priestess of Lloth and turned into a drider. When we unknowingly attacked the ritual procession bringing her back into the city, my character recognized her and opted to spare her life despite initially fleeing from the party.

Either way, to cut a long story short, the cleric, with magic and patience, basically rehabilitated and restored some of her "humanity", and together, got revenge on the nobleborn bitch that transformed her into an eight-legged monstrosity; not that he cared all that much in the end. He was even able to convert her to a True Neutral alignment, 'though that was further down the road, and even after they married.

I romanced a sea hag in 5e to keep her from trying to kill the party. We PROBABLY could have taken her, but I didn't want to take the chance , and the DM had until that point ignored my elderly knight's preference for older women and want of a lady to put on a pedestal entirely.
The group had a fucking blast describing all the awful things that happened and groaning all at once. In the end we had to sacrifice a VERY powerful magic item (Nine Lives Stealer) to get her to let my character go. They must have really liked my character to let me do it, we needed the sword pretty bad later.

Will Chise gain any personality as the series will make a progress? I like Elias, most of the supporting cast, worldbuilding, I even can endure insufferable jew-shota villian, but protagonist is incredibly bland.

The ninja kept sneaking into the villain's private quarters and bed, and killing off his mistresses until he accepted her.

Different game, the bard fell in love with a spider god and I suppose it was mutual. In any case she had a giant spider following her around and protecting her, because she lured him away from the spider goddess with promises not to kill and eat him, and he was absolutely thrilled with that. The outcome was not so good though because it eventually led to demigod half-spiders who were generally not good.

Not really.

Generally, my villains don't start the game thinking too highly of the players if they even acknowledge them in the first place. They typically aren't interested in playing nice from the get go.

By the time the players are on the villain's radar enough to actually merit deepening the relationship, they've typically antagonized the villains too much for romance to be possible.

Well to be fair he's also kind of a psycho.