BL manhwa refers to Boys' Love comics or graphic novels that come from South Korea and feature romantic or intimate relationships between male characters.
Well, a rut bl manhwa usually features male-male romantic relationships and explores various themes related to love and emotions. It's a popular genre in the world of manga.
I'm not entirely sure as I haven't read it specifically. But generally, a side story might expand on the relationships or events that were only hinted at in the main 'stranger than friends' story.
To survive as a villain in a BL manhwa, you have to be strategic. Understand the weaknesses of the heroes and exploit them. Also, build alliances when it suits you, but be ready to betray them if necessary.