Ok so Woojung and Sarang are twins. Jinwoo is in love with Woojung (who is in love with Seohee) but because he's drunk he confess to Sarang (who's gay). Also Seohee likes Jinwoo so it's a love triangle ig.
edit: OMG I JUST FINISHED IT AND IT'S SO CUTE! WORTH READING
Tied Up In Twins