Sounds like love or hate
This one kinda
http://www.mangago.zone/read-manga/renai_nante_yurushimasen/
the mc has a brother complex and thinks that his brother and his best friend are getting together but it ends up being a misunderstanding
i've read that, but i don't want to continue it until it's marked as complete. my anxiety soars to the heavens everytime i read that (⌒▽⌒)
thank you! i haven't actually read this one~
a love triangle which involves, a mc < mc's best friend < mc's younger sibling. i'm kinda interested if there's a story with this kind of flow. buy the mc's best friend and the mc ends up together, not the other way around