I'm looking for Boy x girl friendship, where both the boy and the girl already have partners, but their chemistry with each other, their act around each other is just better than with their boyfriend/girlfriend, that the people around them think that they are dating each other instead of their respective partners. Any?
I rarely read BG but just wanted to have fun and see if I could find someone. The best I could do is still miles away from your request, but why not try? Its a story about the FL who is very much in love with her fiance, and her fiance who doesn't love her. So they are each others "respective partners". But her fiance and the FLs little sister have more chemistry and everyone ships those two. So in this engagement, the ML and FL are an official pair (but not actually dating) But ML is shipped with FL's sister (these two are actually in love) And later on FL finds her own happiness ( Spoiler she finds love too! ) This is like a really really really depressing and sad story (HE) though, so its not funny/lighthearted at all. https://www.novelupdates.com/series/my-fiance-is-in-love-with-my-little-sister
Do readers count? Yamada and the 7 Witches manga had a lot of readers who preferred Yamada with -insert character here- over canon interest Shiraishi.