Another theme might be subverting traditional storytelling. By favoring the villainess, it goes against the normal narrative where the heroines are always the 'good' ones. This can lead to exploring different moral and ethical concepts.
The protagonist who favors the villainess can also be quite interesting. Their reasons for siding with the villainess, whether it's because they see something special in her or they want to change the story's course, can add depth to the character.
A common trait is also being manipulative. The villainess will try to manipulate the situations and the people around her to get what she wants. She might manipulate the male leads by lying about the protagonist or creating misunderstandings between them to drive a wedge in their relationship.
You can try some popular e - book platforms like Amazon Kindle, or check your local library's digital collection if they have a wide range of novels available. Sometimes, official websites of the publisher also provide options for reading.
You can try searching on popular fanfiction websites like Archive of Our Own (AO3). It has a large collection of fanfics, and you might be able to find some great 'I'm in love with the villainess' fanfics there. Just use the search function and type in the relevant keywords.
Honestly, finding a reliable source for raw manga can be tricky. It's not recommended to seek them from unauthorized places. Sometimes, libraries or subscription-based manga services might offer what you're looking for legally.