try:
Another Miss Oh - there is a main couple but there are two side couples who get quite some screen time later in the story
Age Of Youth - story about a friendship and lives of 5 girls. some of them are in relationship, some of them get into relationship. it is really good story
Reply 1997 - there are two main couples
Reply 1988 - there are at least 3 main couples i think (also, both reply 1997 and 1988 are incredibly good dramas. i recommned with my whole heart!)