So this is going to be strangely specific. There's a Taiwanese drama called Love Forward that follows this trope. We are led to believe that the original couples were going to be endgame (they were ok but boring) but then nearly halfway some personal circumstances happen that forces them to swap partners unwillingly. Next thing you know you're shipping the new couple more than the old one LOL. By changing up the partners, I found it a lot more interesting.

Like I said, very specific. I don't mind which country the drama comes from (if there even is another drama that follows this formula) but there must be no cheating involved. 

Maybe:

  • Into the sunlight - old kdrama

Neither of these fit exactly, but they each have dynamics that sort of involves swapping love lines / pairings between the main couple and second couple:

 Czakhareina:

Maybe:

  • Into the sunlight - old kdrama

Thank you, I will look into it.

 AH :

Neither of these fit exactly, but they each have dynamics that sort of involves swapping love lines / pairings between the main couple and second couple:

Ah I see. I know about CLOY but not High Society. I’ll research about it more. So far it’s looking like there’s no other drama that follows this trope.

 Rien:

Secret maybe?

I love Secret! I can see why it might fall into this trope but not to the extent of Love Forward.