Brother seems more like a respectful term used to address ur close senior or someone older than u, doesn't really have to be blood related ! Kinda like how chinese use gege or the koreans use hyung or sunbae
idk who lied to you but this is original work, it doesn't have a novel and its not a love triangle so he ends up with kim woojin (the one in the cover)
This could have been the best chasing arc ever if the author wasn’t rushing it but I would say the story is pretty good