Romantasy Event - Falling For The Villain

Admit it. You love a good villain love story! I know I do. 
This trope has been used in many stories over the years, where the villain falls for the hero, and it changes them for the better. Some popular examples are Spike from Buffy the Vampire Slayer, Damon from Vampire Diaries and Captain Hook from Once Upon A Time.
So what makes it so appealing? For me personally, I like seeing the villain falter. When they go to act on instinct and then stop because they know that it won't be well received by the hero. Of course the fact that they realize this, shows that they are fully aware that their actions are wrong, but they do it anyway.
We do love a good villain in a story, but I think seeing them grow and change is interesting. They may start off trying to kill the hero or at the very least hating them, but somewhere along the way, they fall for them. Forced proximity is often used, along with a bigger villain threatening them all which makes them join forces.
I am a fan of the trope myself, I even released a set earlier this years called Villains Need Love Too. It was a limited set so sadly it has been taken down, but the premise was a villain falling for either a hero or another villain. It was fun to write and it allows you to go to darker places as a writer. Villains don't care about the rules or doing the right thing and often when they first help the hero, they have no choice in the matter. Over time they get closer to the hero and they usually get together.
Can I share an unpopular opinion though? I don't think a lot of the villains deserve their 'happy ending'. Not all, but some of them don't. While I think it is important that they change, the fact that it comes from their feelings for another person makes it seem like that changes is dependent on them. In other words, if they break up or the hero dies, what is stopping them from simply returning to how they were before? That's not true change in my eyes. That is restraining yourself to please someone else. 
A great example of both sides is Stefan and Damon Salvatore from the Vampire Diaries - the show, not the books - because they show two sides of the same coin. Stefan changed on his own, he stuck to it and even after his relationship with Elena ended, he didn't return to being the villain. His growth wasn't dependent on her. Damon's, however, was. When Elena went into her magical coma, he immediately started killing again. While they would be separated, he was going to see her again eventually. Yet he did it anyway. I know the ending of that show was altered to have a 'happy' ending, but I don't believe Damon should have survived. I think he should have died with Stefan.
I know there are some hardcore Spuffy shippers out there too, but I think that was the right ending for Spike. I don't think the two of them belonged together. Of course there was a lot going on behind the scenes and certain scenes should never have happened. 
However, one of my favorite shows - Once Upon A Time - has Captain Hook get his happy ending and I do think he deserved that. I think falling for Emma made him care again, but it wasn't contingent on them being together. He did try to be better. 
So while I love a good villain love story, I believe the villain really has to want to change for themselves and not for another person. They can start them on their journey, but it is up to the villain to keep themselves on it. 
I do notice that in most cases villains are male. So a special mention to Regina from Once Upon A Time. She had a long journey back from being a villain, but it was shown in a way that was believable and her redemption was earned. I think that shows a well developed character, that it is not a case of I've fallen for someone and now I'm going to be a good guy. It is not as simple as that. The villain must fight against their own instincts and work on themselves constantly in order to prevent themselves from slipping back.
These are definitely points to consider if you are writing a villain love story. And please do write some female villains! There aren't enough to read about.

Happy writing!