So the male and female lead are in that limbo between friendship and lovers. They like each other, but haven't started a romance yet. The second leads are pursing both of them. The second male lead comes onto the female lead and the male lead witnesses it. This drives him into the arms of the second female lead. The female lead gets mad at the second male lead and tries to win the male lead back. She eventually does after proving that she's got nothing to do with the second male lead.  

Hard to remember anything that has a whole plot based on it but heres some dramas that have this as a part of their plt maybe covered in 2-3 episodes max.

20th Century Boy and Girl - The FL has a crush on the ML brother but its nothing more than that the ML gets a little angry and stops going after her and attends a marriage date with someone else but when he sees the FL again he goes back after her.

Something About 1 Percent They date as a contract for some time after the contract ends they both try to date other people but they realize the still like each other this gets covered in like the last 2 episodes rest of the drama is nothing about it.

Because This is My First Life The second couple has something like this but not the main couple.