Do you know any manga (any genre), i.e. in shoujo where you have the main couple (boy A and girl B) and then have boy C who falls for girl A and is a love rival to boy A (readers may hate him) BUT of course he gets rejected. Then you have girl D who wants boy A but again fails (again readers may be biased and hate her).

NOW, I would love to see boy C and girl D finding love with each other, like really! Not being substitute for the main couple but actually falling for each other!

Basically I'm tired of seeing those rejected love rivals ending up alone, which is most often the case. Often I end up caring more for them than the boring/stupid main couple

Mochiron, Isharyou Seikyuu itashimasu! Hasn't happened yet but there is foreshadowing.
Marmalade Boy Read it many years ago but if I remember right the side characters end up together or maybe only in the anime.