They flirt all the way to the end, only to discover that the other person is their love rival.
Basically, two people who can't stand each other are both pursuing the same girl. When they discover she plays online games, they both head into the game to chase after her.
They each mistakenly believe the other is their first love (or secret crush), and that their first love (or secret crush) is their love rival. So every day, they deliberately or inadvertently provoke their "rival," then sweetly show off their affection in front of them...
The girl they're secretly in love with: ...This game is so stressful!
Also known as "Love Dies the Moment You Meet."
After meeting in person, they discover that the person they've been dating online for six months is their love rival, while the "rival" they've been going out of their way to annoy is actually the girl they're trying to pursue.
Both of them stare blankly at the knowing look the girl gives them: No, no, let us explain! It's not what you think! (Erkang reaches out.)
Fattened and then slaughtered. Come on, author!